Video multiplexing system for superimposition of scalable video data streams upon a background video data stream

ABSTRACT

A video multiplexing system for superimposition of scalable video data streams upon a background data stream and having a video decoder to extract a first luminance signal, an A/D converter to convert the first luminance signal to digital form, a three-port video memory for storing digitized luminance signal, a D/A converter for receiving the stored digitized luminance signal and converting it to analog form, a mixing or multiplexing means, having one input coupled to the D/A converter output, at least one other luminance signal source as an input and controlling inputs for directing the selection of one of the input luminance signals as an output, and a control means such as a microprocessor for controlling the various components. The write operations to the video memory are synchronized to the incoming luminance signal, and the read operations from the video memory are synchronized to the display device. This video multiplexing architecture provides the ability to open a viewport of arbitrary size at any position within a larger display. Scaling of the digitized luminance signal to fit in a viewport of arbitrary size is achieved by varying the frequency of the A/D converter clocks so as to expand or shrink the resulting image.

This is a continuation of application Ser. No. 08/185,155 filed Jan. 29,1994, which is a continuation of application Ser. No. 08/039,708 filedMar. 31, 1993, which is a continuation of application Ser. No.07/873,322 filed Apr. 14, 1992, which is a continuation of applicationSer. No. 07/474,768 filed May 14, 1990, now abandoned.

TECHNICAL FIELD

The present invention relates to an image processing circuit in themonitor of a personal computer, an intelligent terminal, a TV telephoneor a smart TV and, more particularly, to a process for processing animage to an arbitrary size and superposing it.

BACKGROUND TECHNIQUE

In the prior art, there is an image processing system which is enabledto operate a personal computer while observing a TV program bysuperimposing the picture of the TV with a predetermined size and in apredetermined position on the monitor frame of the personal computer.

FIG. 21 is a block diagram showing the image processing system of theprior art. In FIG. 21: reference numeral 100 designates a video decoderfor separating a first video signal VS₁ into a first synchronizingsignal SS₁ and a first luminance signal LS₁ ; numeral 200 designates ananalog-digital converter (which will be shortly referred to as an "ADC")for digitizing the first luminance signal LS₁ ; numeral 300 designates avideo memory for storing the digitized first luminance signal LS₁ ;numeral 340 designates a write control unit for controlling the writingof the first luminance signal LS₁ in the video memory 300; numeral 350designates a read control unit for controlling the reading of the firstluminance signal LS₁ out of the video memory 300; numeral 400 designatesa digital-analog converter (which will be shortly referred to as a"DAC") for converting to analog the first luminance signal LS₁ read outfrom the video memory 300; numeral 600 designates a CPU control unit;numeral 630 designates a multiplexer; numeral 640 designates a videodecoder unit for separating a third video signal VS₃ into a thirdsynchronizing signal SS₃ and a third luminance signal LS₃ ; and numeral500 designates a mixing control unit for mixing the first luminancesignal LS₁ and the third luminance signal LS₃ to output a fourthluminance signal LS₄,

In this video processing circuit of the prior art, the video decoder 100separates the video signal VS₁ into the synchronizing signal SS₁ and theluminance signal LS₁, and the ADC 200 digitizes and writes the luminancesignal LS₁ in the video memory 300.

At this time, the write control unit 340 outputs a timing clock forcontrolling the operations of the ADC 200 and the video memory 300 onthe basis of the synchronizing signal SS₁.

Here, the second luminance signal LS₂ outputted from the CPU controlunit 600 can be written in the video memory 300.

Moreover, the read control unit 350 reads out the first. Luminancesignal LS₁ (or the second luminance signal LS₂) written in the videomemory 300 through the multiplexer 630. The DAC 400 converts to analogthe first luminance signal LS₁ read out from the video memory 300. Themixing control unit 500 mixes the first luminance signal LS₁ and thethird luminance signal LS₃ to output the fourth luminance signal LS₄ inwhich an image corresponding to the first luminance signal LS₁ issuperimposed on the image corresponding to the third luminance signalLS₃.

For a still image, on the other hand, a CPU 620 monitors the operationsof the video decoder unit 100. If this video decoder unit 100 outputs avertical synchronizing signal, the CPU 620 interrupts the digitizecontrol by the ADC 200 during the vertical blanking period in the videosignal.

In this still image, too, there can be obtained the fourth luminancesignal LS₄ in which the image corresponding to the first luminancesignal LS₁ is superimposed upon the image corresponding to the thirdluminance signal LS₃.

When, moreover, letters or special shapes are to be superimposed uponthe image corresponding to the first luminance signal LS₁, the CPUcontrol unit 600 writes the shape data of the letters or special shapesin the video memory 300.

Here, the image processing system of the prior art, as shown in FIG. 21,is troubled by a problem that it cannot cope in the least with themultipurpose specifications such as the display by an arbitraryresolution corresponding to a smart image to be developed in the nearfuture, the conversion of an arbitrary aspect ratio, the control ofdisplay in an arbitrary position, or the superimpose.

For the multi-purpose specifications, moreover, the price for the systemrises as high as several hundreds to thousands yens as in the TVbroadcasting system used at present in the commercial broadcastingstations.

This raises a problem that fundamental technical innovations arerequired for the level of the home appliances.

Generally speaking, on the other hand, the video memory 300 has to berefreshed because it is constructed of a dynamic memory.

For this necessity, a clock signal for refreshing the video memory 300is fed to the serial ports of the video memory 300. This clock signalhas a frequency of 10 (MHz) or more, for example.

In case, therefore, the serial output at the side of the multiplexer 630has a clock of several hundreds (KHz) to several (MHz), a frequency of10 (MHz) or more has to be supplied from the aforementioned serialoutput other than that at the side of the DAC 400.

This serial output other than that at the side of the DAC 400 has to bemerely the refreshing clock aiming at no output.

If the video data of the video memory 300 is to be read out by the CPUcontrol unit 600, the multiplexer 630 has to be switched to read out thevideo data from the CPU control 600 so that the video data are not sentto the DAC 400. This raises another problem that the image coming fromthe DAC 400 becomes the fourth luminance signal LS₄ in the blanked stateeven if it is superimposed upon the third luminance signal LS₃.

Still another problem is that it is impossible for the CPU to read theCPU control 600 by the operations always having a frequency of 10 (MHz)or more than that of the aforementioned serial output other than that atthe side of the DAC 400.

For the still image, moreover, the CPU control unit 600 has to monitorthe a vertical synchronizing signal VS₁ thereby to raise a furtherproblem that the CPU control unit 600 has to require a standby time ofseveral tens mS in the worst case.

Even if, moreover, the CPU control unit 600 is equipped with ahigh-speed IC such as a digital signal processor (which is called the"DSP"), it takes several tens (μs) to rewrite the letters or specialshapes.

In case, on the other hand, the third luminance signal LS₃ is related toone corresponding to a motion picture, there is required a time periodfor reducing the frame number of the third luminance signal LS₃ and torewrite the stored content of the video memory 300 by the CPU 620.

It is impossible to scroll the letters or special shapes vertically andhorizontally in the third luminance signal LS₃.

DISCLOSURE OF THE INVENTION

The present invention has been conceived to solve the above-specifiedproblems and has an object to provide an image processing system forachieving the following objects:

(1) to realize an arbitrary resolution of the image, an arbitrary areadesignation; a location of an arbitrary memory or a conversion to anarbitrary aspect ratio easily at the level of home appliances;

(2) to read out the luminance signals of the video memory easily from acontrol system of irregular time such as the CPU without anyinterruption of the monitor output function of the video memory;

(3) to eliminate any necessary for the standby for the still image bythe CPU control unit 600;

(4) to rewrite the displayed content in real time on the superimposeddisplay frame; and

(5) to realize the above-specified functions at the price at the levelof the home appliances.

According a first mode of the present invention, there is provided animage processing system comprising: decode means for separating a firstvideo signal into a first luminance signal, a first horizontalsynchronizing signal and a first vertical synchronizing signal;analog-digital conversion means for digitizing said first luminancesignal; memory means for storing the digitized first luminance signal;digital-analog conversion means for reading and analogly converting theluminance signal stored by said memory means; mixing means for eitherthe luminance signal read out and analogly converted by said memorymeans or a second luminance signal selectively as a third luminancesignal; and control means for outputting control signals to control saiddecode means, said analog-digital conversion means, said memory means,said digital-analog conversion means and said mixing means.

In a second mode of the present invention, said analog-digitalconversion means, said memory means, said digital-analog conversionmeans, said mixing means and said control means are constructed on aextended slot card.

In a third mode of the present invention, said control means includes:operation means for inputting the position, size and timing fordisplaying an image corresponding to said first luminance signal to animage corresponding to said third luminance signal; and a device driverdisposed in an operating system for outputting the signals correspondingto the position, size and timing, which are to be inputted by saidoperating means, to said decode means, said memory means, saiddigital-analog conversion means and mixing means.

According to a fourth mode of the present invention, said memory meansIncludes a video memory for storing the first luminance signal, which isdigitized by said analog-digital conversion means, in an area of theaddress, which is specified by a write shift signal and a write lineincrement signal, when a write enable signal is outputted, such that ahorizontal address is reset by a horizontal write clear signal whereas avertical address is reset by a vertical write clear signal, when saidfirst luminance signal is to be written, so that said horizontal addressis set at the unit of a block of a predetermined dot number by anaddress signal and incremented by said write shift signal and so thatsaid vertical address is incremented by said write increment signal, andsaid analog-digital conversion means includes: an analog-digitalconversion circuit for analog-digital converting said first luminancesignal; a horizontal write dot clock generator synchronized with saidfirst horizontal synchronizing signal for outputting a horizontal writedot clock signal having a frequency predetermined times as high as thatof said first horizontal synchronizing signal and based upon said blockunit as the analog-digital conversion clock signal of saidanalog-digital conversion means and a basic synchronizing signal having;a predetermined frequency as said write shift signal; a horizontal writestarting counter reset by said first horizontal synchronizing signal forcounting; the clock number of said horizontal write dot clock signal tooutput a horizontal write starting; signal for starting; the writing; ofsaid first luminance signal in said image memory and said horizontalwrite clear signal when said counted value reaches a preset value; ahorizontal write number counter reset by said first horizontalsynchronizing signal for counting; the clock number of said horizontalwrite dot clock signal, after the output of said horizontal writestarting; signal, to output a horizontal write number signal forinhibiting; the write of said first luminance signal in said videomemory when said counted value reaches a predetermined value; a verticalwrite offset counter reset by said first vertical synchronizing; signalfor outputting a vertical write offset signal of the clock number of thepreset value, which is synchronized with said basic synchronous signal,as said write line increment signal; a vertical write line clockgenerator synchronized with said first vertical synchronizing; signalfor outputting a vertical write line clock signal having a frequency ofpredetermined times as high as that of said vertical synchronizingsignal as said write line increment signal; a vertical write startingcounter reset by said first vertical synchronizing signal for countingthe clock number of said first horizontal synchronizing signal to outputa vertical write starting signal for starting the writing of saidluminance signal in said video memory when said counted value reaches apreset value; a vertical write number counter reset by said verticalsynchronizing signal for starting the counting of the clock number ofsaid vertical write line clock signal, after the output of said verticalwrite starting signal, to output a vertical write number signal forinhibiting the writing of said first luminance signal in said videomemory when said counted value reaches a preset value; and write controlmeans for outputting said write enable signal on the basis of said firstvertical synchronizing signal, said horizontal write clear signal, saidhorizontal write dot clock signal, said horizontal write startingsignal, said horizontal write number signal, said vertical writestarting signal, said vertical write number signal and said verticalwrite line clock signal to write the first luminance signal, which isdigitized by said horizontal write dot clock signal, in the area of saidvideo memory, which is specified by said address signal, said writeshift signal and said write line increment signal, while said horizontalwrite starting signal and said vertical write starting signal are beingoutputted.

In a fifth mode of the present invention, said control means sets thevalue of said block, the frequency of said vertical write line clocksignal, the preset value of said horizontal write starting counter, thepreset value of said horizontal write number counter, the preset valueof said vertical write starting counter and the preset value of saidvertical write number counter.

In a sixth mode of the present invention, said control means includesimage still means for outputting said first vertical synchronizingsignal none of said video memory, said vertical write offset counter,said vertical write line clock generator, said vertical write startingcounter and said vertical write number counter in accordance with theoperations of said operation means.

In a seventh mode of the present invention, said memory means includes:a write control unit for controlling said video memory when said controlmeans writes said second luminance signal in said video memory;luminance signal selecting means for outputting said first luminancesignal and said second luminance signal selectively to said videomemory; and a video memory control signal selecting unit for outputtinga write control signal of said first luminance signal and a writecontrol signal of said second luminance signal in a manner to correspondto the selected output of said first luminance signal and said secondluminance signal.

In an eighth mode of the present invention, said memory means includes:an FIFO memory of first-in first-out type having at least a storagecapacity equal to or more than that of said video memory for writing andreading said luminance signals asynchronously in and out of said videomemory; a read control unit for controlling the reading of saidluminance signal in said FIFO memory out of said video memory inaccordance with the control of said control means; and an FIFO readcontrol unit for controlling said FIFO memory.

In a ninth mode of the present invention, said video memory reads outsaid luminance signal from the address, which is specified by a readshift signal and a read line increment signal of said video memory, whena read enable signal is outputted, such that the horizontal addressreset by said horizontal read clear signal whereas the vertical addressis reset by the vertical read clear signal or said third verticalsynchronizing signal, when said luminance signal stored in said videomemory is to be read out, so that said horizontal address is incrementedby said read shift signal whereas said vertical address is incrementedby said read line increment signal, said digital-analog conversion meansincludes: a digital-analog conversion circuit for analogly convertingand outputting the luminance signal which is read out from said videomemory; a horizontal reference read dot clock generator for outputting ahorizontal reference read dot clock signal synchronized with said thirdhorizontal synchronizing signal; a first horizontal read startingcounter reset by said third horizontal synchronizing signal for countingthe clock number of said horizontal reference read dot clock signal tooutput a first horizontal read starting signal for starting the readingof said luminance signal from said video memory and a horizontal readreset signal as said horizontal read clear signal when said countedvalue reaches a preset value; a second horizontal read starting counterreset by said third horizontal synchronizing signal for counting theclock number of said horizontal reference read dot clock signal, afterthe output of said first horizontal read starting signal, to output thesecond horizontal read starting signal when said counted value reaches apredetermined value; a horizontal read number counter reset by saidthird horizontal synchronizing signal for counting the clock number ofsaid horizontal reference read dot clock signal to inhibit the readingof the luminance signal, which is stored in said video memory, when saidcounted value reaches a preset value; a horizontal read dot clockgenerator for outputting a horizontal read dot clock signal synchronizedwith said third horizontal synchronizing signal; a vertical read offsetcounter reset by said third vertical synchronizing signal for outputtingthe vertical read offset signal as said vertical line increment signalon the basis of said horizontal reference read dot clock signal; avertical blanking number counter reset by said third verticalsynchronizing signal for counting the clock number of said thirdhorizontal synchronizing signal to output a vertical blanking endingsignal when said counted value indicates that a vertical back porchregion has been passed; a vertical read starting counter reset by saidthird vertical synchronizing signal for counting the clock number ofsaid third horizontal synchronizing signal, after the output of saidvertical blanking ending signal, to output a vertical read startingsignal for starting the reading the luminance signal from said videosignal when said counted value reaches a preset value; a vertical readnumber counter reset by said third vertical synchronizing signal forcounting the clock number of said third horizontal synchronizing signal,after the output of said vertical read starting signal, to output avertical read number signal for inhibiting the reading of the luminancesignal from said video memory, when said counted value reaches a presetvalue; a vertical read line clock generator for outputting the verticalread line clock signal, which is synchronized with said third verticalsynchronizing signal, as said vertical line increment signal; asuperimpose start signal output circuit for outputting a superimposestarting signal on the basis of said second horizontal read startingsignal, said horizontal read number signal, said vertical read startingsignal and said vertical read number signal; and a read enable signaloutput circuit for outputting said read enable signal on the basis ofsaid third vertical synchronizing signal, said horizontal read resetsignal, said vertical read line clock signal and said superimposestarting signal to read out the luminance signal from the area of saidvideo memory, which is specified by either said horizontal referenceread dot clock signal or said horizontal read dot clock signal and saidread line increment signal, and said mixing means includes a videoswitch switched on the basis of said superimpose starting signal forselectively outputting the luminance signal, which is read out from saidvideo memory and analogly converted by said digital-analog conversioncircuit, and said third luminance signal.

In a tenth mode of the present invention, said horizontal reference readdot clock generator constructing the ninth mode of the present inventionincludes a PLL circuit for outputting a signal having a frequencyseveral tens to thousands as high as that of said third horizontalsynchronizing signal, said horizontal read dot clock generator includesa PLL circuit for outputting a signal having a frequency a predeterminednumber of times as high as that of said third horizontal synchronizingsignal, and said vertical read line clock generator includes a PLLcircuit for outputting a signal having a frequency a predeterminednumber of times as high as that of said third vertical synchronizingsignal.

In an eleventh mode of the present invention, said control meansconstructing the tenth mode of the present invention sets the individualclock numbers which are counted by said first horizontal read startingcounter, said horizontal read number counter, said vertical blankingnumber counter, said vertical read starting counter and said verticalread number counter.

In a twelfth mode of the present invention, said video memory reads outsaid luminance signal from the address, which is specified by a readshift signal and a read line increment signal of said video memory, whena read enable signal is outputted, such that the horizontal addressreset by said horizontal read clear signal whereas the vertical addressis reset by the vertical read clear signal or said third verticalsynchronizing signal, when said luminance signal stored in said videomemory is to be read out, so that said horizontal address is incrementedby said read shift signal whereas said vertical address is incrementedby said read line increment signal, said digital-analog conversion meansincludes: a digital-analog conversion circuit for analogly convertingand outputting the luminance signal which is read out from said videomemory; a horizontal reference read dot clock generator for outputting ahorizontal reference read dot clock signal synchronized with said thirdhorizontal synchronizing signal; a first horizontal read startingcounter reset by said third horizontal synchronizing signal for countingthe clock number of said horizontal reference read dot clock signal tooutput a first horizontal read starting signal for starting the readingof said luminance signal from said video memory and a horizontal readreset signal as said horizontal read clear signal when said countedvalue reaches a preset value; a second horizontal read starting counterreset by said third horizontal synchronizing signal for counting theclock number of said horizontal reference read dot clock signal, afterthe output of said first horizontal read starting signal, to output thesecond horizontal read starting signal when said counted value reaches apredetermined value; a horizontal read number counter reset by saidthird horizontal synchronizing signal for counting the clock number ofsaid horizontal reference read dot clock signal to inhibit the readingof the luminance signal, which is stored in said video memory, when saidcounted value reaches a preset value; a horizontal read dot clockgenerator for outputting a horizontal read dot clock signal synchronizedwith said third horizontal synchronizing signal; a vertical read offsetcounter reset by said third vertical synchronizing signal for outputtingthe vertical read offset signal as said vertical line increment signalon the basis of said horizontal reference read dot clock signal; avertical blanking number counter reset by said third verticalsynchronizing signal for counting the clock number of said thirdhorizontal synchronizing signal to output a vertical blanking endingsignal when said counted value indicates that a vertical back porchregion has been passed; a vertical read starting counter reset by saidthird vertical synchronizing signal for counting the clock number ofsaid third horizontal synchronizing signal, after the output of saidvertical blanking ending signal, to output a vertical read startingsignal for starting the reading the luminance signal from said videosignal when said counted value reaches a preset value; a vertical readnumber counter reset by said third vertical synchronizing signal forcounting the clock number of said third horizontal synchronizing signal,after the output of said vertical read starting signal, to output avertical read number signal for inhibiting the reading of the luminancesignal from said video memory, when said counted value reaches a presetvalue; a vertical read line clock generator for outputting the verticalread line clock signal, which is synchronized with said third verticalsynchronizing signal, as said vertical line increment signal; asuperimpose start signal output circuit for outputting a superimposestarting signal on the basis of said second horizontal read startingsignal, said horizontal read number signal, said vertical read startingsignal and said vertical read number signal; and a read enable signaloutput circuit for outputting said read enable signal on the basis ofsaid third vertical synchronizing signal, said horizontal read resetsignal, said vertical read line clock signal and said superimposestarting signal to read out the luminance signal from the area of saidvideo memory, which is specified by either said horizontal referenceread dot clock signal or said horizontal read dot clock signal and saidread line increment signal, and said mixing means includes: comparatormeans for comparing said third luminance signal and a predeterminedreference signal; compared output starting signal output means foroutputting a compared output starting signal for starting the output ofthe compared output of said comparator means; superimpose control meansfor outputting a first superimpose starting signal for starting thesuperimpose of the first luminance signal, which is read out from saidvideo memory and analogly converted by said digital-analog converter,upon said third luminance signal and a second superimpose startingsignal for starting the superimpose of said third luminance signal uponsaid first luminance signal; and superimpose control means forsuperimposing said third luminance signal upon the first luminancesignal, which is superimposed upon said third luminance signal, on thebasis of the compared output of said comparator means, said firstsuperimpose starting signal and said second superimpose starting signal.

In a thirteenth mode of the present invention, said horizontal referenceread dot clock generator constructing the twelfth mode of the presentinvention includes a PLL circuit for outputting a signal having afrequency several tens to thousands as high as that of said thirdhorizontal synchronizing signal, said horizontal read dot clockgenerator includes a PLL circuit for outputting a signal having afrequency a predetermined number of times as high as that of said thirdhorizontal synchronizing signal, and said vertical read line clockgenerator includes a PLL circuit for outputting a signal having afrequency a predetermined number of times as high as that of said thirdvertical synchronizing signal.

In a fourteenth mode of the present invention, said control meansconstructing the thirteenth mode of the present invention sets theindividual clock numbers which are counted by said first horizontal readstarting counter, said horizontal read number counter, said verticalblanking number counter, said vertical read starting counter and saidvertical read number counter.

According to a fifteenth mode of the present invention, there isprovided a digitize control system comprising: an analog-digitalconversion circuit for analog-digital converting said first luminancesignal; a video memory for storing the first luminance signal, which isdigitized by said analog-digital conversion means, in an area of theaddress, which is specified by a write shift signal and a write lineincrement signal, when a write enable signal is outputted, such that ahorizontal address Is reset by a horizontal write clear signal whereas avertical address is reset by a vertical write clear signal, when saidfirst luminance signal is to be written, so that said horizontal addressis set at the unit of a block of a predetermined dot number by anaddress signal and incremented by said write shift signal and so thatsaid vertical address is incremented by said write increment signal; ahorizontal write dot clock generator synchronized with said firsthorizontal synchronizing signal for outputting a horizontal write dotclock signal having a frequency predetermined times as high as that ofsaid first horizontal synchronizing signal and based upon said blockunit as the analog-digital conversion clock signal of saidanalog-digital conversion means and a basic synchronizing signal havinga predetermined frequency as said write shift signal; a horizontal writestarting counter reset by said first horizontal synchronizing signal forcounting the clock number of said horizontal write dot clock signal tooutput a horizontal write starting signal for starting the writing ofsaid first luminance signal in said image memory and said horizontalwrite clear signal when said counted value reaches a preset value; ahorizontal write number counter reset by said first horizontalsynchronizing signal for counting the clock number of said horizontalwrite dot clock signal, after the output of said horizontal writestarting signal, to output a horizontal write number signal forinhibiting the write of said first luminance signal in said video memorywhen said counted value reaches a predetermined value; a vertical writeoffset counter reset by said first vertical synchronizing signal foroutputting a vertical write offset signal of the clock number of thepreset value, which is synchronized with said basic synchronous signal,as said write line increment signal; a vertical write line clockgenerator synchronized with said first vertical synchronizing signal foroutputting a vertical write line clock signal having a frequency ofpredetermined times as high as that of said vertical synchronizingsignal as said write line increment signal; a vertical write startingcounter reset by said first vertical synchronizing signal for countingthe clock number of said first horizontal synchronizing signal to outputa vertical write starting signal for starting the writing of saidluminance signal in said video memory when said counted value reaches apreset value; a vertical write number counter reset by said verticalsynchronizing signal for starting the counting of the clock number ofsaid vertical write line clock signal, after the output of said verticalwrite starting signal, to output a vertical write number signal forinhibiting the writing of said first luminance signal in said videomemory when said counted value reaches a preset value; and write controlmeans for outputting said write enable signal on the basis of said firstvertical synchronizing signal, said horizontal write clear signal, saidhorizontal write dot clock signal, said horizontal write startingsignal, said horizontal write number signal, said vertical writestarting signal, said vertical write number signal and said verticalwrite line clock signal to write the first luminance signal, which isdigitized by said horizontal write dot clock signal, in the area of saidvideo memory, which is specified by said address signal, said writeshift signal and said write line increment signal, while said horizontalwrite starting signal and said vertical write starting signal are beingoutputted.

In a sixteen mode of the present invention, said digitize control systemincludes digitize control means sets the value of said block, thefrequency of said vertical write line clock signal, the preset value ofsaid horizontal write starting counter, the preset value of saidhorizontal write number counter, the preset value of said vertical writestarting counter and the preset value of said vertical write numbercounter.

In a seventh mode of the present invention, said write control meansincludes image still means for outputting said first verticalsynchronizing signal none of said video memory, said vertical writeoffset counter, said vertical write line clock generator, said verticalwrite starting counter and said vertical write number counter inaccordance with the operations of said operation means.

In an eighteenth mode of the present invention, there is provided asuperimpose control system comprising: a video memory storing aluminance signal for reading out said luminance signal from the address,which is specified by a read shift signal and a read line incrementsignal of said video memory, when a read enable signal is outputted,such that the horizontal address reset by said horizontal read clearsignal whereas the vertical address is reset by the vertical read clearsignal or a vertical synchronizing signal, so that said horizontaladdress is incremented by said read shift signal whereas said verticaladdress is incremented by said read line increment signal; adigital-analog conversion circuit for analogly converting and outputtingthe luminance signal which is read out from said video memory; ahorizontal reference read dot clock generator for outputting ahorizontal reference read dot clock signal synchronized with saidhorizontal synchronizing signal; a first horizontal read startingcounter reset by said horizontal synchronizing signal for counting theclock number of said horizontal reference read dot clock signal tooutput a first horizontal read starting signal for starting the readingof said luminance signal from said video memory and a horizontal readreset signal as said horizontal read clear signal when said countedvalue reaches a preset value; a second horizontal read starting counterreset by said horizontal synchronizing signal for counting the clocknumber of said horizontal reference read dot clock signal, after theoutput of said first horizontal read starting signal, to output thesecond horizontal read starting signal when said counted value reaches apredetermined value; a horizontal read number counter reset by saidhorizontal synchronizing signal for counting the clock number of saidhorizontal reference read dot clock signal to inhibit the reading of theluminance signal, which is stored in said video memory, when saidcounted value reaches a preset value; a horizontal read dot clockgenerator for outputting a horizontal read dot clock signal synchronizedwith said horizontal synchronizing signal; a vertical read offsetcounter reset by said vertical synchronizing signal for outputting thevertical read offset signal as said vertical line increment signal onthe basis of said horizontal reference read dot clock signal; a verticalblanking number counter reset by said vertical synchronizing signal forcounting the clock number of said horizontal synchronizing signal tooutput a vertical blanking ending signal when said counted valueindicates that a vertical back porch region has been passed; a verticalread starting counter reset by said vertical synchronizing signal forcounting the clock number of said horizontal synchronizing signal, afterthe output of said vertical blanking ending signal, to output a verticalread starting signal for starting the reading the luminance signal fromsaid video signal when said counted value reaches a preset value; avertical read number counter reset by said vertical synchronizing signalfor counting the clock number of said horizontal synchronizing signal,after the output of said vertical read starting signal, to output avertical read number signal for inhibiting the reading of the luminancesignal from said video memory, when said counted value reaches a presetvalue; a vertical read line clock generator for outputting the verticalread line clock signal, which is synchronized with said verticalsynchronizing signal, as said vertical line increment signal; asuperimpose start signal output circuit for outputting a superimposestarting signal on the basis of said second horizontal read startingsignal, said horizontal read number signal, said vertical read startingsignal and said vertical read number signal; a read enable signal outputcircuit for outputting said read enable signal on the basis of saidvertical synchronizing signal, said horizontal read reset signal, saidvertical read line clock signal and said superimpose starting signal toread out the luminance signal from the area of said video memory, whichis specified by either said horizontal reference read dot clock signalor said horizontal read dot clock signal and said read line incrementsignal; and a video switch switched on the basis of said superimposestarting signal for selectively outputting the luminance signal, whichis read out from said video memory and analogly converted by saiddigital-analog conversion circuit, and said luminance signal.

In a nineteenth mode of the present invention, said horizontal referenceread dot clock generator constructing the eighteenth mode of the presentinvention includes a PLL circuit for outputting a signal having afrequency several hundreds as high as that of said third horizontalsynchronizing signal, said horizontal read dot clock generator includesa PLL circuit for outputting a signal having a frequency a predeterminednumber of times as high as that of said third horizontal synchronizingsignal, and said vertical read line clock generator includes a PLLcircuit for outputting a signal having a frequency a predeterminednumber of times as high as that of said third verticalsynchronizing-signal.

In a twelfth mode of the present invention, said superimpose controlsystem further comprises control means for setting the individual clocknumbers which are counted by said first horizontal read startingcounter, said horizontal read number counter, said vertical blankingnumber counter, said vertical read starting counter and said verticalread number counter.

In a twenty first mode of the present invention, there is provided asuperimpose control system comprising: a video memory storing aluminance signal for reading out said luminance signal from the address,which is specified by a read shift signal and a read line incrementsignal of said video memory, when a read enable signal is outputted,such that the horizontal address reset by said horizontal read clearsignal whereas the vertical address is reset by the vertical read clearsignal or a vertical synchronizing signal, so that said horizontaladdress is incremented by said read shift signal whereas said verticaladdress is incremented by said read line increment signal; adigital-analog conversion circuit for analogly converting and outputtingthe luminance signal which is read out from said video memory; ahorizontal reference read dot clock generator for outputting ahorizontal reference read dot clock signal synchronized with saidhorizontal synchronizing signal; a first horizontal read startingcounter reset by said horizontal synchronizing signal for counting theclock number of said horizontal reference read dot clock signal tooutput a first horizontal read starting signal for starting the reading;of said luminance signal from said video memory and a horizontal readreset signal as said horizontal read clear signal when said countedvalue reaches a preset value; a second horizontal read starting counterreset by said horizontal synchronizing signal for counting; the clocknumber of said horizontal reference read dot clock signal, after theoutput of said first horizontal read starting signal, to output thesecond horizontal read starting; signal when said counted value reachesa predetermined value; a horizontal read number counter reset by saidhorizontal synchronizing signal for counting the clock number of saidhorizontal reference read dot clock signal to inhibit the reading of theluminance signal, which is stored in said video memory, when saidcounted value reaches a preset value; a horizontal read dot clockgenerator for outputting a horizontal read dot clock signal synchronizedwith said horizontal synchronizing signal; a vertical read offsetcounter reset by said vertical synchronizing signal for outputting thevertical read offset signal as said vertical line increment signal onthe basis of said horizontal reference read dot clock signal; a verticalblanking number counter reset by said vertical synchronizing signal forcounting the clock number of said horizontal synchronizing signal tooutput a vertical blanking ending signal when said counted valueindicates that a vertical back porch region has been passed; a verticalread starting counter reset by said vertical synchronizing signal forcounting the clock number of said horizontal synchronizing signal, afterthe output of said vertical blanking ending signal, to output a verticalread starting signal for starting the reading the luminance signal fromsaid video signal when said counted value reaches a preset value; avertical read number counter reset by said vertical synchronizing signalfor counting the clock number of said horizontal synchronizing signal,after the output of said vertical read starting signal, to output avertical read number signal for inhibiting the reading of the luminancesignal from said video memory, when said counted value reaches a presetvalue; a vertical read line clock generator for outputting the verticalread line clock signal, which is synchronized with said verticalsynchronizing signal, as said vertical line increment signal; asuperimpose start signal output circuit for outputting a superimposestarting signal on the basis of said second horizontal read startingsignal, said horizontal read number signal, said vertical read startingsignal and said vertical read number signal; a read enable signal outputcircuit for outputting said read enable signal on the basis of saidvertical synchronizing signal, said horizontal read reset signal, saidvertical read line clock signal and said superimpose starting signal toread out the luminance signal from the area of said video memory, whichis specified by either said horizontal reference read dot clock signalor said horizontal read dot clock signal and said read line incrementsignal; comparator means for comparing said third luminance signal and apredetermined reference signal;

compared output starting signal output means for outputting a comparedoutput starting signal for starting the output of the compared output ofsaid comparator means; superimpose control means for outputting a firstsuperimpose starting signal for starting the superimpose of the firstluminance signal, which is read out from said video memory and analoglyconverted by said digital-analog converter, upon said third luminancesignal and a second superimpose starting signal for starting thesuperimpose of said third luminance signal upon said first luminancesignal; and superimpose control means for superimposing said thirdluminance signal upon the first luminance signal, which is superimposedupon said third luminance signal, on the basis of the compared output ofsaid comparator means, said first superimpose starting signal and saidsecond superimpose starting signal.

In a twenty second mode of the present invention, said horizontalreference read dot clock generator of the twenty first mode of thepresent invention includes a PLL circuit for outputting a signal havinga frequency several hundreds as high as that of said third horizontalsynchronizing signal, said horizontal read dot clock generator includesa PLL circuit for outputting a signal having a frequency a predeterminednumber of times as high as that of said third horizontal synchronizingsignal, and said vertical read line clock generator includes a PLLcircuit for outputting a signal having a frequency a predeterminednumber of times as high as that of said third vertical synchronizingsignal.

In a twenty third mode of the present invention, said superimposecontrol system further comprises control means for setting theindividual clock numbers which are counted by said first horizontal readstarting counter, said horizontal read number counter, said verticalblanking number counter, said vertical read starting counter and saidvertical read number counter.

According to the first mode of the present invention thus constructed,the decoding means separates the first video signal into the firstluminance signal, the first horizontal synchronizing signal and thefirst vertical synchronizing signal and analog-digital converts them,and the memory means stores the digitized first luminance signal.

Moreover, the digital-analog conversion means converts the digitizedluminance signal stored in the memory means to analog and the mixingmeans reads it out from the memory means so that either the analoglyconverted luminance signal or the second luminance signal is selectivelyoutputted as the third luminance signal.

The aforementioned operations are controlled by the control means.

According to the second mode of the present invention thus constructed,moreover, the decoding means, the analog-digital conversion means, thememory means, the digital-analog conversion means, the mixing means andthe control means constructing the first mode of the present inventionare constructed over the one extended slot card.

According to the third mode of the present invention thus constructed,furthermore, the operation means inputs the position, size and timing ofdisplaying the image corresponding to the first luminance signal withrespect to the image corresponding to the third luminance signal. Then,the signal corresponding to the position, size and timing inputted tothe device drive in the OS is outputted to the decode means, the memorymeans, the digital-analog conversion means and the mixing means.

According to the fourth mode of the present invention thus constructed,furthermore, the write enable signal is outputted on the basis of thefirst vertical synchronizing signal, the horizontal write clear signal,the horizontal write dot clock signal, the horizontal write startingsignal, the horizontal write number signal, the vertical write startingsignal, the vertical write number signal and the vertical write lineclock signal. While the horizontal write starting signal and thevertical write starting signal are being outputted, the first luminancesignal, which is digitized by the horizontal write dot clock signal, iswritten in the area of the video memory, which is specified by theaddress signal, the write shift signal and the write line incrementsignal.

According to the fifth mode of the present invention thus constructed,furthermore, when the operations of the fourth mode of the presentinvention are to be accomplished, the control means sets the value ofthe block, the frequency of the vertical write line clock signal, thepreset value of the horizontal write starting counter, the preset valueof the horizontal write number counter, the preset value of the verticalwrite starting counter, and the preset value of the vertical writenumber counter.

According to the sixth mode of the present invention thus constructed,furthermore, the still image means does not output the first verticalsynchronizing signal to the video memory, the vertical write offsetcounter, the vertical write line clock generator, the vertical writestarting counter and the vertical write number counter in accordancewith the operations of the operation means.

According to the seventh mode of the present invention thus constructed,when the write control unit writes the second luminance signal in thevideo memory, the write control means controls the video memory. Then,the luminance signal selection means outputs the first luminance signaland the second luminance signal selectively to the video memory. Thevideo memory control signal selection unit outputs the write controlsignals of the first luminance signal and the second luminance signalselectively in response to the selected output of the first and secondluminance signals.

According to the eighth mode of the present invention thus constructed,furthermore, the read control unit and the FIFO read control unitcontrol the reading of the luminance signal from the video memory intothe FIFO memory in accordance with the control of the control means.

According to the ninth mode of the present invention thus constructed,furthermore, the read enable signal output circuit outputs the readenable signal on the basis of the third vertical synchronizing signal,the horizontal read reset signal, the vertical read line clock signaland the superimpose starting signal to read out the luminance signalfrom the area of the video memory, which is specified by either thehorizontal reference read dot clock signal or the horizontal read dotclock signal and the read line increment signal. Then, the video switchis switched on the basis of the superimpose starting signal toselectively output the luminance signal, which is read out from thevideo memory and analogly converted by the digital-analog converter, andthe third luminance signal.

According to the tenth mode of the present invention thus constructed,furthermore, the aforementioned horizontal reference read dot clockgenerator, the horizontal read dot clock generator and vertical readline clock generator are constructed of PLL circuits.

According to the eleventh mode of the present invention thusconstructed, furthermore, the control means the individual clock numbersto be counted by the first horizontal read starting counter, thehorizontal read number counter, the vertical blanking number counter,the vertical read starting counter and the vertical read number counter.

According to the twelfth mode of the present invention thus constructed,furthermore, the luminance signal, which is analogly converted by thedigital-analog converter, and the third luminance signal are selectivelyoutputted like the ninth mode of the present invention.

According to the fifteenth mode of the present invention thusconstructed, furthermore, the first luminance signal digitized by thehorizontal write dot clock signal is written line the fourth mode of thepresent invention in the area of the video memory, which is specified bythe address signal, the write shift signal and the write line Incrementsignal.

According to the eighteenth mode of the present invention thusconstructed, furthermore, the luminance signal, which is read out fromthe video memory and analogly converted by the digital-analog converter,and the third luminance signal are selectively outputted like the ninthmode of the present invention.

According to the twenty first mode of the present invention thusconstructed, furthermore, the luminance signal, which is analoglyconverted by the digital-analog converter, and the third luminancesignal are selectively outputted like the twelfth mode of the presentinvention.

As has been described hereinbefore, according to the present invention,the decode means separates the first video signal into the firstluminance signal, the first horizontal synchronizing signal and thefirst vertical synchronizing signal and subjects them to theanalog-digital conversions. Moreover, the digital-analog conversionmeans analogly converts the luminance signal, which is stored in thememory means, and the mixing means reads out it from the memory means tooutput either the converted to analog luminance signal or the secondluminance signal selectively as the third luminance signal. Thus, therecan be attained an effect to provide an image processing system capableof displaying an image corresponding to the first luminance signal in adesired position, with a desired size and at a desired timing withrespect to the image corresponding to the second luminance signal.

Since, moreover, the individual component means are constructed over theone extended slot card, it is possible to provide a compact imageprocessing system.

Thus, on the basis of the first vertical synchronizing signal, thehorizontal write clear signal, the horizontal write dot clock signal,the horizontal write starting signal, the horizontal write numbersignal, the vertical write starting signal, the vertical write numbersignal and the vertical write line clock signal, the write enable signalis outputted so that the first luminance signal can be written in adesired position and with a desired size, while the horizontal writestarting signal and the vertical write starting signal are beingoutputted, in the area of the video memory, which is specified by theaddress signal, the write shift signal and the write line incrementsignal.

Furthermore, the first vertical synchronizing signal is not outputted tothe video memory, the vertical write offset counter, the vertical writeline clock generator, the vertical write starting counter and thevertical write number counter so that a still image can be easilyobtained.

Furthermore, not only the first luminance signal but also the secondluminance signal outputted from the control means can be written.

Furthermore, the control means can easily read the first luminance meansin accordance with the control of the control means without obstructingthe output of that first luminance signal to the monitor.

Furthermore, the video switch is switched on the basis of thesuperimpose starting signal to selectively output the first luminancesignal, which is read out from the video memory and converted to analogby the digital-analog converter, and the third luminance signal.

Furthermore, it is possible to accomplish the so-called "doublesuperimpose", in which the first luminance signal is superimposed uponthe third luminance signal whereas the third luminance signal is furthersuperimposed upon the first luminance signal. Thus, the switching ismade on the basis of the signal so that the first luminance signal,which is read out from the video memory and converted to analog by thedigital-analog converter, and the third luminance signal can beselectively outputted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing an image processing systemaccording to one embodiment of the present invention;

FIG. 2 is an external view showing the image processing system shown inFIG. 1;

FIG. 3 is an external view showing a personal computer body in which anextended slot card shown in FIG. 2 is built;

FIG. 4 is a detailed block circuit diagram showing a major portion ofthe image processing system shown in FIG. 1;

FIG. 5 is a connection diagram between the extended slot card shown inFIG. 2 and a tuner;

FIG. 6 is a diagram for explaining the operations of the imageprocessing system shown in FIG. 1;

FIG. 7 is a memory map;

FIG. 8 is a circuit diagram showing a digitize control unit shown inFIG. 4 and its peripheral circuits;

FIG. 9 is a timing chart showing the operations of the digitize controlunit shown in FIG. 4 and its peripheral circuits;

FIG. 10 is a circuit diagram showing a DMA circuit shown in FIG. 4;

FIG. 11 is a timing chart showing the operations of the DMA circuitshown in FIG. 4;

FIG. 12 is a circuit diagram showing an offset circuit;

FIG. 13 is a timing chart showing the operations of the offset circuitshown in FIG. 12;

FIG. 14 is a circuit diagram showing a superimpose control circuit shownin FIG. 4 and its peripheral circuits; and

FIGS. 15, 16, 17 and 18 are timing charts showing the operations of thesuperimpose control unit shown in FIG. 14 and its peripheral circuits;

FIG. 19 is a circuit diagram showing a multiplex superimpose controlunit;

FIG. 20 is a timing chart showing the operations of the multiplexsuperimpose control unit shown in FIG. 19; and

FIG. 21 is a block diagram showing the image processing system of theprior art.

THE BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail in the following inconnection with one embodiment thereof with reference to theaccompanying drawings.

FIG. 1 is a schematic block diagram showing showing an image processingsystem according to the embodiment of the present invention. In FIG. 1:reference numeral 100 designates a video decoder for separating either avideo signal VSTV coming from a (not-shown) tuner or a video signal VSEX(which will be referred simply as the "video signal VSTV") coming from a(not-shown) external device such as a VTR into a luminance signal LSTVand a synchronizing signal SSTV; numeral 200 designates an ADC controlunit for digitizing the luminance signal LSTV; numeral 300 designatesthree-port video memory control unit for storing the digitized luminancesignal LSTV; numeral 400 designates a DAC control unit for reading out aluminance signal LSMEM from the three-port video memory control unit 300to convert it to analog; numeral 500 designates a video mixing controlunit for mixing the luminance signal LSMEM read out from the three-portvideo memory control unit 300 and analogly converted and a luminancesignal LSPC outputted from a personal computer, a work station, aterminal, a game machine or the like (which will be shortly referredaltogether to the "personal computer", although not shown) to output aluminance signal LSMON in which an image corresponding to the luminancesignal LSTV is superimposed in an image corresponding to the luminancesignal LSPC; and numeral 600 designates a CPU control unit foroutputting control data through a data bus 610 to the video decoder 100,the ADC control unit 200, the three-port video memory control unit 300,the DAC control unit 400 and the video mixing control unit 500.

These control data outputted from the CPU control unit 600 are those forachieving the luminance signal LSMON according to an object and arecontrolled by the CPU control unit 600.

Next, FIG. 2 is a perspective view showing the image processing systemshown in FIG. 1. In FIG. 2: reference numeral 700 designates a personalcomputer body; numeral 701 designates a personal computer monitor;numeral 702 designates a keyboard; numeral 703 designates a mouse;numeral 704 designates an extended slot card forming the major portionof the image processing system; numeral 705 designates an inter-bodyvideo cable for connecting the personal computer body 700 and theextended slot card 704; numeral 706 designates an inter-monitor videocable for connecting the personal computer monitor 701 and the extendedslot car 704; numeral 710 designates a tuner; and numeral 711 designatesan antenna.

This image processing system has a structure, in which the extended slotcard 704 is interposed between the personal computer body 700 and thepersonal computer monitor 701.

The extended slot card 704 is connected with the tuner 710 and insertedinto the (not-shown) extended slot of the personal computer body 700, asshown in FIG. 3.

The image corresponding to the luminance signal LSTV outputted from thetuner 710 is displayed together with the image corresponding to theluminance signal LSPC, with an arbitrary size, at an arbitrary timing inan arbitrary position of the image corresponding to the luminance signalLSPC and displayed by the personal computer monitor 701, by theoperation of the keyboard 702 or the mouse 703.

Next, FIG. 4 is a detailed block circuit diagram showing the majorportion of the image processing circuit shown in FIG. 1. In FIG. 4:reference numeral 101 designates an audio signal terminal for inputtingan audio signal ASEX outputted from the VTR or the like; numeral 110designates an audio signal selector for selectively outputting the audiosignal ASEX inputted from the audio signal terminal 101 and an audiosignal ASTV inputted from the tuner 710; numeral 120 designates a volumecontrol circuit for controlling the volume of the audio signal ASTV;numeral 102 designates an audio signal terminal for outputting theselected audio signal ASTV as an audio signal ASMON of the personalcomputer monitor 701; numeral 103 designates a video signal terminal forinputting a video signal VSEX outputted from the VTR or the like;numeral 130 designates a video signal selector for selectivelyoutputting the video signal VSEX inputted from the video signal terminal103 and a video signal VSTV inputted from the tuner 710; and numeral 140designates a video signal decoder for separating the selectivelyoutputted video signal VSTV into the luminance signal LSTV and asynchronizing signal SSTV.

Moreover, numeral 210 designates an ADC for digitizing the luminancesignal LSTV; and numeral 220 designates a digitize control unit forcontrolling the ADC 210 and so on on the basis of the synchronizingsignal SSTV.

Moreover, numeral 310 designates a three-port video memory having onewrite port and two read ports numeral 320 designates a video dataselector for selectively outputting either the luminance signal LSTVoutputted from the ADC 210 or the luminance signal LSPC outputted fromthe (not-shown) personal computer; numeral 330 designates a video memorycontrol signal selector for selectively outputting either a video memorycontrol signal WETV outputted from the digitization control unit 220 ora video memory control signal WEPC outputted from a write control unit340; this write control unit 340 is used for controlling the luminancesignal LSPC outputted from the personal computer in the three-port videomemory 310; numeral 350 designates a read control unit; numeral 360designates a first-in/first-out type FIFO memory for storing theluminance signal LSMEM stored by the three-port video memory 310; andnumeral 370 designates a FIFO read control unit for controlling the readof the luminance signal LSMEM coming from the three-port video memory310.

On the other hand, numeral 410 designates a DAC; numeral 420 designatesa superimpose control unit for controlling the three-port video memory310, the DAC 410 and an AND circuit 530 by inputting a synchronizingsignal HSPC and a vertical synchronizing signal VSPC outputted from thepersonal computer; numeral 510 designates a video switch for outputtingeither of the luminance signal LSPC coming from the personal computer orthe luminance signal LSMEM coming from the three-port video memory 310as the luminance signal LSMON of the personal computer monitor; numeral520 designates a mixing control unit; numeral 540 designates a voltagecomparator for comparing a reference voltage V_(r) and the luminancesignal LSPC coming from the personal computer; and numeral 620designates a CPU in the personal computer body.

Next, FIG. 5 is a connection diagram for connecting the tuner 710 andthe extended slot card 704. In FIG. 5: numeral 712 designates a tunercontrol connector for outputting the control signal such as the powersource or tuning signal of the tuner 710 to the tuner 710; numeral 713designates an output connector for outputting the audio signal ASTVoutputted from the tuner 710 to the extended slot card 704; and numeral714 designates an output connector for outputting the video signal VSTVoutputted from the tuner 710 to the extended slot card 704.

Here, the audio signal ASTV can be outputted to a headphone 717 or a(not-shown) speaker through a plug 716 connected with an outputconnector 715.

The tuner 710 outputs the audio signal ASTV and video signal VSTV ofspecified channels of the signals it receives from the antenna 711 andthe antenna terminal, to the audio signal selector 110 and the videosignal selector 130, respectively, through the output connectors 713 and714.

In this case, the tuning is accomplished by controlling the CPU 620.

On the other hand, the audio signal ASEX and the video signal VSEX areoutputted from a (not-shown) video device such as a video deck or alaser disc, respectively, to the audio signal selector 110 and the videosignal selector 130.

The audio input selector 110 is controlled by the CPU 620 to select andoutput the audio signal ASTV or ASEX to the volume control circuit 120.

This volume control circuit 120 is controlled by the CPU 620 to amplifythe audio signal ASTV outputted from the audio signal selector 110 andto output it as the audio signal ASMON in the personal computer monitorcable to the audio signal terminal 102.

The audio signal ASTV is outputted to the output connector 714.

The video signal selector 130 is controlled by the CPU 620 to select andoutput the video signal VSTV or VSEX to the video signal decoder 140.

FIG. 6 is a diagram for explaining the operations of the present imageprocessing system. The image displayed in the display frame 301 of thepersonal computer monitor corresponding to the video signal obtainedfrom the tuner 710 is displayed in a reduced scale to move at arighthand upper portion.

The display area is assigned by mouse cursor 301 using mouse 703. Theimage obtained from tuner 710 is displayed in the assigned display area.

FIG. 7 shows a memory map in which the OS or MS-DOS (as known under thetrade name) of the personal computer is packaged as the used in-OSdevice driver (or the front processor) by using the utility software ofthe present invention.

Thanks to this packaging, the utility software can be run to observe theimage from the TV set or the video deck in a preferable position andwith a preferable size by a simple keyboard operation no matter whatapplication software is operating on the OS.

The video signal decoder 140 separates the video signal VSTV, which isoutputted from the video signal selector 130, into the luminance signalLSTV and the synchronizing signal SSTV and outputs them to the ADC 210and the digitize control unit 220 respectively, as shown in FIG. 4.

Here the synchronizing signal SSTV is composed of the verticalsynchronizing signal VSTV and a horizontal synchronizing signal HSTV.

In response to a clock signal CKAD outputted from the digitize controlunit 220, the ADC 210 converts the luminance signal LSTV outputted fromthe video signal decoder 140 into a digital signal and outputs itthrough the video data selection unit 320 to the three-port video memory310.

The digitization control unit 220 outputs not only the clock signal CKADto the ADC 210 but also the video memory control signal WETV through thevideo memory control signal selection unit 330 to the three-port videomemory 310.

Thus, the three-port video memory 310 stores the updated luminancesignal LSTV under the condition controlled by the CPU 620.

FIG. 8 is a block diagram diagram showing the digitize control unit 220shown in FIG. 4 and its peripheral circuits.

Here is omitted the video memory control signal selector 330. In thepresent embodiment, the three-port video memory 310 is exemplified bythe product CSK1206 of SONY and the product MB81C1501 of FUJITSU.

Incidentally, the following description will be made by using only theread ports of the three-port video memory 310.

The characteristic timing chart is disclosed on pp. 21 to 26 of the DataSheet 71215-ST of SONY.

The three-port video memory 310 is constructed to have a capacity of 960columns ×306 rows ×4 bits.

As a result, one effective horizontal scanning period can be quantizedwith the numerical value of 960.

On the other hand, the three-port video memory 310 is accessed for thecolumns at the unit of block and for the rows at the unit of line.

In the three-port video memory 310: reference characters DIN0 to DIN3designate data inputs for inputting the luminance signal LSTV;characters ADD0 to ADD3 designate address inputs; characters CKW0designate a port-0 shift signal; characters INC0 designate a port-0 lineincrement signal; characters HCLR0 designate a port-0 horizontal clearsignal; characters VCLRO designate a port-0 vertical clear signal; andcharacters WE (i.e., negative logic) designate a port-0 write enablesignal.

These signals CKW0, VCLR0, HCLR0, INC0 and WE (i.e., negative logic),ADDO and DIN0 to DIN3 are dichroic video signals of 4 bits, i.e., 16gradations.

Here, even color luminance signals of 4 bits or more could naturally belikewise handled by connecting a plurality of three-port video memories310 in parallel.

In FIG. 8: reference numeral 140 designates the video signal decoder forseparating the video signal VSTV into the horizontal synchronizingsignal HSTV, the vertical synchronizing signal VSTV and the luminancesignal LSTV to output them; numeral 221 designates a dot clock generatorfor outputting a horizontal write dot clock signal HDCK and a basicsynchronizing signal BSYNC; numeral 222 designates a horizontal writestarting counter for outputting a horizontal write starting signal HWSand an HCLRO signal; numeral 223 designates a horizontal write numbercounter for outputting a horizontal write number signal HWT; numeral 224a vertical write line clock generator for outputting vertical write lineclock signal VWLCK; numeral 225 designates, a vertical write startingcounter for outputting a vertical write starting signal VWS; numeral 226designates a vertical write number counter for outputting vertical writenumber signal VWT; numeral 227 designates a vertical write offsetcounter for outputting a vertical write offset signal VWOFT fordesignating the vertical write position of the three-port video memory310 and the port-0 line increment INC0; numeral 228 designates an ORcircuit for outputting either the vertical write line clock signal VWLCKor the vertical write offset signal VWOFT as the port-0 line incrementINC0; numeral 229 designates an AND circuit for taking the logicalproduct of the inverted outputs of the horizontal write dot clock signalHDCK, the horizontal write starting signal HWS and the horizontal writenumber signal HWT and the inverted outputs of the vertical writestarting signal VWS and the vertical write number signal VWT to output awrite enable signal WENBL; and numeral 230 designates a NOR circuit fortaking the output of AND 810, the HCLRO signal, the output signal of theOR circuit 228 and the write enable signal WENBL outputted from the ANDcircuit 229 to output the port-0 write enable signal WE.

Incidentally for the color display, the luminance signal LSTV iscomposed of individual R, G and B luminance signals RLSTV, GLSTV andBLSTV.

The video signal decoder 140 separates the video signal VSTV outputtedfrom the video signal selector 130, into the horizontal synchronizingsignal HSTV, the vertical synchronizing signal VSTV and the luminancesignal LSTV.

The horizontal synchronizing signal HSTV is outputted to the dot clockgenerator 221, the horizontal write starting counter 222, the horizontalwrite number counter 223 and the vertical write starting counter 225.

The vertical synchronizing signal VSTV is outputted to the verticalwrite line clock generator 224, the vertical write starting counter 225,the vertical write number counter 226, the vertical write offset counter227, the port-0 vertical clear terminal VCLR0 of the three-port videomemory 310, and the NOR circuit 230.

Moreover, the luminance signal LSTV is outputted to the ADC 210.

This ADC 210 digitizes the luminance signal LSTV1 in response to thehorizontal write dot clock signal HDCK, which is inputted as the clocksignal CKAD, to output the digitized the luminance signal LSTV to thethree-port video memory 310.

The dot clock generator 221 generates the horizontal write dot clocksignal HDCK having a period of 1/N (N: a post five integer) insynchronism with the horizontal synchronizing signal HSTV, i.e., theperiod 63.5 μs of the horizontal synchronizing signal HSTV. Thehorizontal write dot clock signal HDCK is outputted to the ADC 210, thehorizontal write starting counter 222, the horizontal write numbercounter 223 and the AND circuit 229.

In case the block unit of the address preset of the three-port videomemory 310 is 60 dots whereas one effective horizontal scanning periodof the vertical synchronizing signal VSTV is 50 (μ s), the horizontalwrite dot clock signal HWDCK has its frequency calculated, as follows:

60 (dots)/50·10⁻⁶ (S)=1.2 (MHz).

By this horizontal write dot clock signal HDCK, one effective horizontalscanning period can be quantized with 60 dots.

Since the three-port video memory 310 is constructed to have sixteenblocks (=960 dots for 60 dots composing one block), the luminance signalLSTV of one effective horizontal scanning period can be written at theunit of block, as follows:

    1.2 (MHz)×16 (blocks)=19.2 (MHz)

Thus, the dot clock generator 221 outputs the horizontal write dot clocksignal HDCK having the frequency based upon the value of the block B.

Here, the value of the block B can be set by the CPU 620.

Moreover, the dot clock generator 221 generates a basic synchronizingsignal BSYNC to be used as the clock of the port-0 shift signal terminalCKW0 (for incrementing the horizontal write address of the three-portvideo memory 310 at the unit of dot) of the three-port video memory 310.

As a result, the image corresponding to the luminance signal LSTV isenlarged when the period of the clock signal CKAD for digitizing theluminance signal LSTV is longer than that of the basic synchronizingsignal BSYNC for incrementing the horizontal write address of thethree-port video memory 310 at the unit of dot. When, on the contrary,the period of the clock signal CKAD is smaller than that of the basicsynchronizing signal BSYNC, the image corresponding to the luminancesignal LSTV is reduced.

The basic synchronizing signal BSYNC is one for synchronizing theindividual control circuits basically and is outputted to the horizontalwrite starting counter 222, the horizontal write number counter 223, thevertical write line clock generator 224, the vertical write startingcounter 225, the vertical write number counter 226, the vertical offsetcounter 227 and the three-port video memory 310.

The vertical write line clock generator 224 is synchronized with thevertical synchronizing signal VSTV to output the vertical write lineclock signal VWLCK having a frequency an N times as high as that of thevertical synchronizing signal VSTV to the vertical write number counter226 and the OR circuit 230.

Incidentally, the value of N can be set by the CPU 620. The value of Nis determined on the basis of an aspect ratio suitable for the dot clockgenerator 221.

The horizontal write starting counter 222 is reset by the horizontalsynchronizing signal HSTV to count the clock number of the horizontalwrite dot clock signal HWDCK thereby to output the horizontal writestarting signal HWS starting the quantization of the luminance signalLSTV at the S₁ -th clock for the effective horizontal scanning period ofthe video signal VSTV.

The horizontal write starting counter 222 outputs one clock of theport-0 horizontal Clear signal HCLRO together with the horizontal writestarting signal HWS to and circuit 229.

The horizontal write time counter 223 starts the counting of the clocksof the horizontal write dot clock signal HWDCK, when it is reset by thehorizontal synchronizing signal HSTV to output the horizontal writestarting signal HWS, to output the horizontal write number signal HWTallowing the quantization of the luminance signal LSTV only for theperiod of the E₁ clocks of the effective horizontal scanning period ofthe luminance signal VSTV.

Thus, the horizontal write number counter 223 controls the effectivehorizontal scanning period.

The vertical write starting counter 225 is reset by the verticalsynchronizing signal VSTV to count the clock number of the horizontalsynchronizing signal HSTV thereby to output the vertical write startingsignal VWS allowing the quantization of the luminance signal LSTV of theeffective horizontal scanning from the S₂ -th clock of the verticaleffective scanning period of the video signal VSTV.

The vertical write number counter 226 starts the counting of the clocksof the vertical write line clock signal VWLCK, when the vertical writestarting signal VWS is outputted, to output the vertical write numbersignal VWT allowing the quantization of the luminance signal LSTV forthe period of the clocks E₂ of the vertical effective scanning period ofthe video signal VSTV.

Thus, the vertical write number counter 226 controls the verticaleffective scanning period.

The write position in the horizontal direction, i.e., in the COLUMNdirection of the three-port video memory 310 with respect to the displayframe is determined by a block designation, in which the sixty bits ofthe quantized luminance signal LSTV is one block, in accordance with anaddress preset mode.

This block designation is accomplished at sixteen steps in response toaddress input signals ADD0 to ADD3.

These address input signals ADD0 to ADD3 can be set by the CPU 620.

The vertical write position of the three-port video memory 310 is set bythe vertical write offset counter 227.

The vertical write offset counter 227 is reset by the verticalsynchronizing signal VSTV and the counter outputs the vertical writeoffset signal VWOFT for offsetting the vertical write position of thethree-port video memory 310 in synchronism with the basic synchronizingsignal BSYNC thereby to control the vertical write position of thethree-port video memory 310.

Here, these values of S₁, E₁, S₂, E₂ and S₃ are set by the CPU 620.

Next, the operations of the digitize control unit 220 and its peripheralcircuits shown in FIG. 8 will be described in the following withreference to the timing chart of FIG. 9.

(1) When the vertical synchronizing signal VSTV takes a high level "H"(as shown at (a) in FIG. 9), the vertical write starting counter 225,the vertical write number counter 226 and the vertical write offsetcounter 227 are reset to set the vertical write starting signal VWS andthe vertical write number signal VWT at a low level "L" (as shown at (d)and (e) in FIG. 9).

(2) The vertical write offset counter 227 outputs basic synchronizingsignal BSYNC as the vertical write offset signal VWOFT for the period ofthe S₃ clocks (as shown at (h) in FIG. 9).

The vertical write offset signal VWOFT is outputted through the ORcircuit 228 to the port-0 line increment signal terminal INCO so thatthe three-port video memory 310 has its vertical address incremented bythe S₃ times.

(3) When the clock number of the vertical synchronizing signal VSTVtakes the value S2, on the other hand, the vertical write startingcounter 225 raises the vertical write starting signal VWS to the highlevel "H" to allow the quantization of the vertical effective scanningperiod (as shown at (d) in FIG. 9).

(4) The three-port video memory 310 has its vertical write offset, whenit receives the clocks of the vertical write offset signal VWOFT so thatthe horizontal synchronizing signal HSTV takes the high level "H". Then,the horizontal write starting counter 222 and the horizontal writenumber counter 223 are reset to drop the horizontal write startingsignal HWS and the horizontal write number signal HWT to the low level"L" (as shown at (n) and (o) in FIG. 9).

On the other hand, the dot clock generator 221 outputs the horizontalwrite dot clock signal HWDCK (as shown at (m) in FIG. 9).

In response to the output of the horizontal write dot clock signalHWDCK, the ADC 210 uses the horizontal write dot clock signal HWDCK asthe sampling hold signal and the data latch signal to sample theluminance signal LSTV.

The horizontal write starting counter 222 counts the number of cycles ofthe horizontal write dot clock signal HWDCK to raise the horizontalwrite starting signal HWS to the high level "H", when the counted valuereaches S₁, thereby to allow the quantization of the effectivehorizontal scanning period (as shown at (n) in FIG. 9).

Simultaneously with this, the horizontal write start counter 222 outputsone clock of the port-0 horizontal clear signal HCLRO of the three-portvideo memory 310 to prepare the writing operations.

At this time, the AND circuit 229 takes the logical product conditionamong the horizontal write starting signal HWS at the high level "H",the inverted horizontal write number signal HWT at the low level "L",the vertical write starting signal VWS at the high level "H" and theinverted vertical write number signal VWT at the low level "L" to outputthe horizontal write dot clock signal HWDCK as the write enable signalWENBL to the NOR circuit 230.

Then, this NOR circuit 230 takes the NOT-OR condition among the port-0horizontal clear signal HCLRO at the high level "H" the verticalsynchronizing signal VSTV at the high level "H", the vertical writeoffset signal VWOFT or the vertical write line clock signal VWLCK at thehigh level "H" and the write enable signal WENBL to output the writeenable signal WE to the write enable signal terminal WE of thethree-port video memory 310.

In response to the output of the write enable signal WE, the three-portvideo memory 310 writes the luminance signal LSTV outputted from the ADC210.

Simultaneously with this, the horizontal write number counter 223 countsthe clock number of the horizontal write dot clock signal HWDCK to allowthe write of the luminance signal LSTV till the counted value reachesE₁.

When this counted value reaches E₁, the horizontal write number counter223 raises the horizontal write number signal HWT to the high level "H"to inhibit the write (as shown at (o) in FIG. 9).

While the luminance signal LSTV is being written, the line addresses inthe common vertical direction are written in the horizontal directiontill the vertical write line clock generator 224 outputs the verticalwrite line clock signal VWLCK.

When the vertical write line clock generator 224 outputs the verticalwrite line clock signal VWLCK as the port-0 line increment signalterminal INCO of the three-port video memory 310, the write line addressof the three-port video memory 310 in the vertical direction advances by1.

When the clock number of the vertical write line clock signal VWLCKoutputted to the vertical write number counter 226 from the verticalwrite line clock generator 224 reaches the value E₂, the vertical writenumber counter 226 raises the vertical write number signal VWT to thehigh level "H" to interrupt the writing of the three-port video memory310 for the vertical effective scanning period (as shown at (e) in FIG.9).

This interruption of writing is continued till the verticalsynchronizing signal VSTV takes another round of the high level "H".

In the present embodiment thus far described, the smart image can berealized, although difficult in the prior art, by controlling thecontrol signals to be outputted to the ADC 210 and the three-port videomemory 310, with respect to the single signal flow.

Incidentally, the active logic is effected by the high level "H" in theaforementioned operations but may be likewise accomplished by the lowlevel "L".

According to the present embodiment, the imaging techniques such as thearbitrary resolution of the video signal VSTV, the arbitrary aspectratio, the window display of the arbitrary region or the multi-strobostill image can be easily controlled by the CPU 620, and the productioncost can be easily dropped for home appliances. Therefore, the imageprocessing system can be used in not only a video device such as apersonal computer TV set, an intelligence terminal, a TV telephone or asmart TV set but also an area designated monitor system using a videomonitor camera and is indispensable in a future machine associated withimages.

The three-port video memory 310 accomplishes the following operations incase the CPU 620 writes video data.

First of all, the CPU 620 controls a change-over control signal CC ofthe write control unit 340 to switch the video data selection unit 320and the video memory control signal selection unit 330.

As a result of this switching, the three-port video memory 310 receivesnot a write control signal WCTV outputted from the digitize control unit220 but a write control signal WCPC outputted from the write controlunit 340.

The luminance signal LSPC outputted from the CPU 620 is inputted throughthe write control unit 340 and the video data selection unit 320 to thethree-port video memory 310.

The three-port video memory 310, is written with that luminance signalLSPC in response to the write control signal WCPC outputted from thewrite control unit 340.

Next, the three-port video memory 310 transfers the luminance signal tothe FIFO memory 360 by the DMA transfer.

FIG. 10 is a block circuit diagram showing the three-port video memory310, the FIFO memory 360, the FIFO DMA control unit 370 all relating tothat DMA transfer, and their peripheral circuits.

Here, the FIFO memory 360 has a storage capacity equal to or more thanthat of the three-port video memory 310.

Here will be described the operations in which the CPU 620 reads out thestored luminance signal LSMEM of the three-port video memory 310 by theDMA.

First of all, the read control unit 350 controlled by the CPU 620outputs the scanning line information or the offset value of thescanning line, which is to be read out from the three-port video memory310, to the three-port video memory 310.

The FIFO read control unit 370 subjects the three-port video memory 310to the direct memory access (which will be shortly referred to the"DMA") with the luminance data LSMEM of the canning line to transfer theluminance signal LSMEM to the input port of the asynchronous I/O or theFIFO memory 360.

The CPU 620 reads in the luminance signal LSMEM thus transferred to theFIFO memory 360, from the output port of the FIFO memory 360 through theread control unit 350 and the CPU bus 610.

Incidentally, the present invention can naturally be embodied if thepersonal computer body and the personal computer monitor are integrated,although the present embodiment has been described in the case of thepersonal computer body and the personal computer monitor beingseparated.

Next, the operations of the DMA circuit shown in FIG. 10 will bedescribed in the following with reference to the timing chart of FIG.11.

(1) When the FIFO DMA control unit 370 outputs the horizontal clearsignal HCLR, which is used to reset the horizontal address of thethree-port video memory 310, through a luminance data bus 371 to thethree-port video memory 310 (as shown at (b) in FIG. 11), the three-portvideo memory 310 is set at a 0 address.

When, on the other hand, the FIFO read control unit 370 outputs theaddress reset signal FRR (i.e., the signal inverted from the horizontalclear signal HCLR by a NOT circuit 372) of the FIFO memory 360 to theFIFO memory 360 simultaneously with the output of the horizontal clearsignal HCLR (as shown at (d) in FIG. 11), the write address of the FIFOmemory 360 is set at the 0 address.

(2) Each time the clock signal CLK outputted from the FIFO control unit370 rises after the setting of the three-port video memory 310 (as shownat (a) in FIG. 11), this three-port video memory 310 outputs theluminance signal LSMEM (as shown at (c) in FIG. 11) so that the FIFOmemory 360 reads in the luminance signal LSMEM outputted from thethree-port video memory 310.

(3) Each time the clock signal CLK rises (as shown at (a) in FIG. 11),the addresses of both the three-port video memory 310 and the FIFOmemory 360 are incremented one by one so that the reading of theluminance signal LSMEM from the three-port video memory 310 and thewriting of the luminance signal LSMEM in the FIFO memory 360 arerepeatedly executed.

(4) When the reading and writing of the luminance signal LSMEM areaccomplished by the N times (i.e., the maximum number of repetitions),the FIFO read control unit 370 outputs the horizontal clear signals HCLRand FRR to set the addresses of the three-port video memory 310 and theFIFO memory 360 to the 0 address so that the aforementioned operationsare repeated.

Since, in this case, the clock signal CLK outputted from the FIFO DMAcontrol unit 370 is given a frequency no less than 10 MHz by thespecifications of the reading condition of the three-port video memory310, it is used as the refresh timing of the three-port video memory310.

Next, FIG. 12 is a circuit diagram showing an offset circuit for readingout a luminance signal LSFIFO from the FIFO memory 360 by setting theaddress of the FIFO memory 360, which is stored with the luminancesignal of the three-port video memory 310, at a predetermined address.

The operations of this offset circuit will be described with referenceto the timing chart of FIG. 13.

(1) The CPU 620 sets the read offset value N of the FIFO memory 360 inthe read control unit 350 through the CPU bus 610.

(2) If the CPU 620 outputs an FIFO read memory set signal RR at the highlevel "H" (as shown at (b) in FIG. 13, the counter in the FIFO readcontrol unit 350 and the read address in the FIFO memory 360 are set tothe 0 address.

In response to the output of the FIFO read memory reset signal RR,moreover, an FIFO read offset starting signal CST for starting the clockin the read control unit 350 and an FIFO offset ending signal CEND forending the clock are dropped to the low level "L" so that the CPU 620the clock signal CLK of the N clocks to the FIFO memory 360 and the FIFOread control unit 350.

(3) After the clock signal CLK has been outputted by the N clocks (asshown at (a) in FIG. 13), the FIFO read control unit 350 raises the FIFOread offset ending signal CEND to the high level "H" (as shown at (d) inFIG. 13) to stop the output of the clock signal CLK to the FIFO memory360 and the FIFO read control unit 350.

At this time, the FIFO memory 360 outputs an N-address luminance signalLSFIFO as the DATA signal at its output portion.

The FIFO read offset ending signal CEND is outputted to the CPU 620,too, so that the CPU 620 reads in the DATA signal in response to thehigh level "H" of a chip select/read signal RD/CS.

(4) When this chip select/read signal RD/CS takes the low level !"L",the FIFO memory 360 has its address incremented by 1.

Since the output portion of the three-port video memory 310 can beoperated with a frequency of 10 (MHz) or higher, as has been describedhereinbefore, the clock signal CLK can be used as the refresh timing ofa dynamic memory of the three-port video memory 310.

Thus, the transfer of the luminance signal LSMEM from the three-portvideo memory 310 to the DAC 410 is not interrupted so that asuperimposed image is always outputted as the luminance signal LSMON tothe personal computer monitor.

Therefore, the present invention can be applied to the promising videoappliances such as the personal computer TV set, the intelligentterminal or the TV telephone.

Incidentally, the logics of the timing chart shown in FIG. 13 are merelyexplanatory and should not be limited thereto.

Moreover, the transfer of the luminance data has been described in thepresent embodiment in the state having the personal computer body andmonitor separated from each other but could be accomplished in case thebody and monitor are integrated into one personal computer.

Next, the superimpose control unit 420 outputs the read control signaland the clock signal CKDA to the three-port video memory 310 and the DAC410 on the basis of the conditions controlled by the CPU 620.

In response to the read control signal, the updated luminance signalLSMEM is read out from the three-port video memory 310.

The DAC 410 converts the luminance signal LSMEM, which is read out fromthe three-port video memory 310, into the analog signal LSDA and outputsit to the video switch 510.

The AND circuit 530 takes an AND condition between the superimposestarting signal outputted from the superimpose control unit 420 and themultiplex super impose starting signal outputted from the mixing controlunit 520 controlled by the CPU 620.

The video switch 510 switched on the basis of the output signal of theAND circuit 530 to superimpose the luminance signal LSMEM outputted fromthe DAC 410 on the personal computer body side luminance signal LSPC.

Next, FIG. 14 is a block circuit diagram showing the superimpose controlunit 420 shown in FIG. 4 and its peripheral circuits. Here is omittedthe AND circuit 530.

Moreover, the three-port video memory 310 is exemplified by theaforementioned product CXK1206 of SONY or MB81C1501 of FUJITSU, and theread port of its three input/output ports is used.

The timing chart is disclosed on pp. 27 to 31 of the data sheet No.71215-ST of the CXK1206 of SONY. The port used is the read port 1appearing on pp. 2.

In the three-port video memory 310: a memory drive clock signal HDCK isinputted to a port-1 shift signal CKR1; a memory vertical/horizontalreset signal MRST is inputted to a port-1 vertical clear VCLR1; ahorizontal reset signal HRST is inputted to a port-1 horizontal clearHCLR1; a vertical offset signal VOFT or a vertical line clock signalVLCK is inputted to a port-1 line increment INC1; and a port-1 outputenable RE1 (i.e., negative logic) is inputted to a port-1 output enableRE1 (i.e., negative logic).

Moreover, the luminance signal LSMEM is read out from port-1 dataoutputs DO₁₀ to DO₁₃.

The luminance signal LSMEM having its read controlled by those port-Ishift signal, CKR1, port-1 vertical clear signal VCLR1, port-1horizontal clear signal HCLR1 port-1 line increment signal INC1, port-1output enable RE1 (i.e., negative logic) and port-1 data outputs DO₁₀ toDO₁₃ is a dichroic luminance signal having 4 bits, i.e., sixteengradations.

Here, it is needless to say that the luminance signal having 4 bits ormore or the color luminance signal could likewise be processed.

In FIG. 14: reference numeral 310 designates a three-port video memoryfor storing the luminance signal LSMEM; numeral 410 designates a DAC forconverting the luminance signal LSMEM to analog prior to outputtingluminance signal LSDA; numeral 510 designates a video switch foroutputting the input at a point A or B from a common point C in responseto a change-over signal CNT inputted to the change-over input terminal;numeral 620 designates a CPU for outputting the horizontal synchronizingsignal HSPC or the vertical synchronizing signal VSPC; numeral 610designates a CPU bus; numeral 421 designates a horizontal reference readdot clock generator for outputting a horizontal reference read dot clocksignal HBDCK; numeral 422 designates a horizontal read starting counterfor outputting a horizontal read starting A signal HRSA and a horizontalread direction reset signal HRST; numeral 423 designates a horizontal64-clock counter for outputting a horizontal read starting B signalHRSB; numeral 424 designates a horizontal read number counter foroutputting a horizontal read number signal HRT; numeral 425 designates ahorizontal read dot clock generator for outputting a horizontal read dotclock signal HDDA; Numeral 426 designates a memory vertical read offsetcounter having a function capable to set the count number of thehorizontal reference read dot clock generator 421 at will by the CPU 820to output a vertical read offset signal VROFT; numeral 427 designates avertical blanking number counter for outputting vertical blanking endingsignal; numeral 428 designates a vertical read starting counter foroutputting a vertical read starting signal VRS; numeral 429 designates avertical read number counter for outputting a vertical read numbersignal VRT; numeral 430 designates a vertical read line clock generatorfor outputting a vertical read line clock signal VRLCK; numeral 431designates an AND circuit for outputting a superimpose starting signal;numeral 432 designates an OR circuit for outputting either a verticalread offset signal VROFT or a vertical read line increment signal VRLCKas a vertical read clear signal VCLR1; numeral 433 designates a NORcircuit for outputting a read enable signal RE1; numerals 434 and 435designate tri-state circuits; and numeral 436 designates an invertercircuit.

The luminance signal LSPC outputted by the personal computer is inputtedto the point A of the video switch 510.

Moreover, the horizontal synchronizing signal HSPC is inputted to thehorizontal reference read dot clock generator 421, the horizontal readstarting counter 422, the horizontal 64-clock counter 423, thehorizontal read number counter 424, the horizontal read dot clockgenerator 425, the vertical blanking number counter 427, the verticalread starting counter 428, the vertical read number counter 429, thevertical read line clock generator 430 and the (not-shown) personalcomputer monitor.

The horizontal read starting counter 422, the horizontal 64-clockcounter 423 and the horizontal read number counter 424 have theirindividual count values reset by the horizontal synchronizing signalHSPC.

Moreover, the vertical synchronizing signal VSPC is inputted to theport-1 vertical clear VCLR1 of the three-port video memory 310, the NORcircuit 433, the vertical read offset counter 426, the vertical blankingnumber counter 427, the vertical read starting counter 428, the verticalread number counter 429, the vertical read line clock generator 430 andthe personal computer monitor.

The vertical read offset counter 426, the vertical blanking numbercounter 427, the vertical read starting counter 428 and the verticalread number counter 429 have their individual count values reset by thevertical synchronizing signal VSPC.

The horizontal reference read dot clock generator 421 is constructed ofa PLL circuit, which is synchronized with the horizontal synchronizingsignal HSPC to output a signal having a frequency several hundreds timesas high as that of the horizontal synchronizing signal HSPC, to outputthe horizontal reference read dot clock signal HBDCK corresponding tothe horizontal dot clock signal of the personal computer monitor.

The horizontal reference read dot clock signal HBDCK is outputted as theclock signal HDCK of the three-port video memory 310 to the port-1 shiftsignal terminal CKR1 of the three-port video memory 310 through thehorizontal read starting counter 422, the horizontal 64-clock counter423, the horizontal read number counter 424, the vertical read offsetcounter 426 and the tri-state circuit 435.

The vertical read dot clock generator 425 is constructed of a PLLcircuit, which is synchronized with the horizontal synchronizing signalHSPC to output a signal having a frequency of N₁ times as high as thatof the horizontal synchronizing signal HSPC, to output the horizontalread dot clock signal HDDA.

The horizontal read dot clock signal HDDA is outputted as the clocksignal HDCK of the three-port video memory 310 through the tri-statecircuit 434 to the port-1 shift signal terminal CKR1 of the three-portvideo memory 310 and the DAC 410 so that it is used as the read clocksignal of the luminance signal LSMEM and the conversion clock signal ofthe DAC 410.

The vertical read line clock generator 430 is constructed of a PLLcircuit, which is synchronized with the vertical synchronizing signalVSPC to output a signal having a frequency of N₂ times as high as thatof the vertical synchronizing signal VSPC, to output the vertical readline clock signal VRLCK.

The vertical read line clock signal VRLCK is synchronized with the clocksignal HDCK of the three-port video memory 310 and is outputted to theport-1 output enable RE1 (i.e., the negative logic) through not only theport-1 line increment INC1, which is used to advance the line address,i.e., the vertical address of the three-port video memory 310 throughthe OR circuit 432, but also the OR circuit 432 and the NOR circuit 433.

The basic timings of the superimpose circuit 420 is obtained by thosehorizontal reference read dot clock signal HBDCK, horizontal read dotclock signal HDDA and vertical read line clock signal VRLCK.

In order to determine the read starting offset point of the three-portvideo memory 310, the vertical read offset counter 426 outputs thevertical offset signal VOFT for summing the vertical line addresses ofthe three-port video memory 310, while being synchronized with thehorizontal reference read dot clock signal HBDCK, after the countedvalue has been reset by the vertical synchronizing signal VSPC.

The vertical blanking number counter 427 outputs the vertical blankingending signal VBE when the (not-shown) counter for eliminating thevertical back porch region of the LSPC counts the clock number of thehorizontal synchronizing signal HSPC so that the vertical back porchregion is passed.

In response to the output of the vertical blanking ending signal VBE orthe starting signal outputted from the vertical blanking number counter427, the vertical read starting counter 428 counts the clock number ofthe horizontal synchronizing signal HSPC to output the vertical readstarting signal VRS or the vertical read starting signal coming from thethree-port video memory 310.

In response to the output of the luminance signal VRS or the startingsignal outputted from the vertical read starting counter 428, thevertical read number counter 429 counts the clock number of thehorizontal synchronizing signal HSPC to output the vertical read numbersignal VRT or the vertical read period coming from the three-port videomemory 310.

This three-port video memory 310 is vertically controlled by thevertical read offset counter 426, the vertical blanking number counter427, the vertical read starting counter 428 and the vertical read numbercounter 429.

Here, the clock number of the horizontal reference read dot clock signalHBDCK counted by the vertical read offset counter 426, the clock numberof the horizontal synchronizing signal HSPC counted by the verticalblanking number counter 427, the clock number of the horizontalsynchronizing signal HSPC counted by the vertical read starting counter428, and the clock number of the horizontal synchronizing signal HSPCcounted by the vertical read number counter 429 can be set at individualarbitrary values by the CPU 620.

Moreover, the horizontal read starting counter 422 counts the clocknumber of the horizontal reference read dot clock signal HBDCK, which isoutputted by the horizontal reference read dot clock generator 421, tooutput the horizontal read starting A signal HRSSA or the horizontalread starting signal of the three-port video memory 310.

In response to the output of the horizontal read starting A signal HRSAor the starting signal outputted from the horizontal read startingcounter 422, a horizontal 64 clock counter 423 counts the clock numberof the reference dot clock signal HBDCK, which is outputted from thehorizontal reference read dot clock generator 421, to output thehorizontal read starting B signal HRSB when the counted value reachesthe 64 clocks or the characteristics at the time of the readingoperation of the three-port video memory 310.

The horizontal read number counter 424 counts the clock number of thereference dot clock signal HBDCK, which is outputted from the horizontalreference read dot clock generator 421, to output the horizontal readnumber signal HRT or the horizontal reading period starting signal ofthe three-port video memory 310.

This three-port video memory 310 is horizontally controlled by thehorizontal read starting counter 422, the horizontal 64 clock counter192 and the horizontal read number counter 424.

Here, the clock number of the horizontal reference read dot clock signalHBDCK counted by the horizontal read starting counter 422 and the clocknumber of the reference dot clock signal HBDCK counted by the horizontalread number counter 424 can be set at individually arbitrary values bythe CPU 620.

Next, the operations of the superimpose control unit 420 will bedescribed in the following with reference to FIGS. 15, 16, 17 and 18.

FIG. 15 is a time chart showing the vertical read starts of thethree-port video memory 310; FIG. 16 is a timing chart showing thevertical offsets of the three-port video memory 310; and FIG. 17 is atiming chart showing the horizontal read starts of the three-port videomemory 310. FIG. 18 is a timing chart showing the horizontal reads ofthe three-port video memory 310.

First of all, the vertical read starts of the three-port video memory310 will be described in the following with reference to FIG. 15.

When the vertical synchronizing,signal VSPC takes the high level "H" (asshown at (a) in FIG. 15), the vertical blanking number counter 427, thevertical read starting counter 428 and the vertical read number counter429 are reset to drop the vertical blanking ending signal VBE, thevertical read starting signal VRS and the vertical read number signalVRT to the low level "L" (as shown at (d), (d) and (f) in FIG. 15). Whenthe vertical blanking number counter 427 counts the clock number of thehorizontal synchronizing signal HSPC to pass the vertical back porchregion, the vertical blanking ending signal VBE is raised to the highlevel "H" (as shown at (d) in FIG. 15).

When the vertical blanking ending signal VBE takes the high level "H"the vertical read starting counter 428 starts to count the clock numberof the horizontal synchronizing signal HSPC.

When the vertical read starting counter 428 counts the set value of theCPU 620, the vertical read starting signal VRS is raised to the highlevel "H" (as shown at (e) in FIG. 15).

When the vertical read starting signal VRS takes the high level "H" thethree-port video memory 310 is allowed to start the reading of theluminance signal LSMEM in the vertical direction so that the verticalread number counter 429 starts to count the clock number of thehorizontal synchronizing signal HSPC.

When the vertical read number counter 429 counts the set value of theCPU 620, the vertical read number signal VRT is raised to the high level"H" (as shown at (f) in FIG. 15).

When the horizontal read starting B signal HRSB is at the high level "H"whereas the horizontal read number signal HRT is at the low level "L",the AND circuit 431 outputs the superimpose starting signal SENBL whilethe vertical reading starting signal VRS is at the high level "H"whereas the vertical read number signal VRT is at the low level "L".

On the basis of the horizontal read start, therefore, the three-portvideo memory 310 reads out the luminance signal LSMEM.

Next, the vertical offsets of the three-port video memory 310 will bedescribed in the following with reference to FIG. 16.

When the vertical synchronizing signal VSPC takes the high level "H" (asshown at (a) in FIG. 16), the vertical read offset counter 426 is resetto start the counting of the clock number of the reference dot clocksignal HBDCK.

The vertical read offset counter 426 outputs the vertical read offsetsignal VROFT, while counting the set value of the CPU 620, through theOR circuit 432 to the port-1 line increment INC1 of the three-port videomemory 310 (as shown at (c) in FIG. 16) to offset the three-port videomemory 310 vertically.

Since, at this time, the vertical synchronizing signal VSPC and thevertical read offset signal VROFT are inputted to the NOR circuit 433,the read enable signal RE1 (i.e., the negative logic) Is also outputtedto the read enable RE1 (i.e., the negative logic) of the three-portvideo memory 310.

Next, the horizontal read starts of the three-port video memory 310 willbe described in the following with reference to FIG. 17.

When the horizontal synchronizing signal HSPC, the horizontal readstarting counter 422, the horizontal 64-clock counter 423 and thehorizontal read number counter 424 are reset to drop the horizontal readstarting A signal HRSA, the horizontal read starting B signal HRSB andthe horizontal read number signal HRT to the low level "L" (as shown at(d), (e) and (f) in FIG. 17).

When the horizontal read starting counter 422 counts the clock number ofthe reference dot clock signal HBDCK, which is outputted by thehorizontal reference read dot clock generator 421, so that the countedvalue takes the set value of the CPU 620, it raises the horizontal readstarting A signal HRSA to the high level "H" (as shown at (d) in FIG.17).

When the horizontal read starting A signal HRSA takes the high level "H"the horizontal 64-clock counter 423 starts to count the clock number ofthe reference dot clock signal HBDCK. When this counted value reaches64, the horizontal read starting B signal HRSB is raised to the highlevel "H" (as shown in FIG. (e) in FIG. 17).

Incidentally, the horizontal 64-clock counter 423 need not its value to64 because this number Is caused from the characteristics of thethree-port video memory 310.

When the horizontal read starting B signal HRSB takes the high level"H", the horizontal read of the three-port video memory 310 is startedso that the horizontal read number counter 424 starts the counting ofthe clock number of the reference dot clock signal HBDCK. When thecounted value reaches the set value of the CPU 620, the horizontal readnumber signal HRT is raised to the high level "H" (as shown at (f) inFIG. 17).

When the vertical read starting signal VRS is at the high level "H"whereas the vertical read number signal VRT is at the low level "L", theAND circuit 431 outputs the superimpose starting signal SENBL at thehigh level "H" while the horizontal read starting B signal is at thehigh level "H" whereas the horizontal read number signal HRT is at thelow level "L".

On the basis of the vertical read start, therefore, the three-port videomemory 310 reads out the luminance signal LSMEM.

Next, the horizontal reading operations of the three-port video memory310 will be described in the following with reference to FIG. 18.

The superimpose starting signal SENBL takes the high level "H" (as shownat (c) in FIG. 18), and the read enable signal RE1 shown is one when theluminance signal LSMEM is read out from the three-port video memory 310and when the DAC 410 is subjected to the analog conversion on the basisof the horizontal read dot clock signal HDDAS outputted from thehorizontal red dot clock generator 425 (as shown at (b) in FIG. 18).

The luminance signal LSPC of the personal computer is inputted to thepoint A of the video switch 510.

Moreover, the luminance signal LSDA read out from the three-port videomemory 310 and converted to analog by the DAC 410 is inputted to thepoint B of the video switch 510.

As a result of the switching of the video switch 510, the luminancesignal LSMON or the output of the video switch 510 is outputted as theluminance signal LSMON corresponding to the image, which is formed bysuperimposing the image corresponding to the analogly convertedluminance signal LSDA upon the image corresponding to the luminancesignal LSPC outputted from the personal computer.

Together with the output of the luminance signal LSMON, the horizontalsynchronizing signal HSFC and the vertical synchronizing signal VSPC arealso outputted to the personal computer monitor.

Incidentally, the timing charts thus far described are presented merelyas one example, and the aforementioned operations can be achieved nomatter whether the individual signals might be positive or negativelogics.

As shown in FIG. 14, on the other hand, when the superimpose startingsignal SENBL at the high level "H" is outputted through the NOT circuit436 to the tri-state circuit 434, this tri-state circuit 434 operates tooutput the horizontal read dot clock signal HDDA as the drive clocksignal HDCK. When the superimpose starting signal SENBL is at the lowlevel "L", the tri-state circuit 435 operates to output the referencedot clock signal HBDCK as the drive clock signal HDCK.

By using the superimpose control unit 420 in the intelligent terminaland home TV set, according to the present invention, the image of the TVtelephone or the interphone can be easily superimposed to realizemonitorless TV telephone or interphone. Thus, one step is advanced torealize a new software computer, in which the image can be freelycontrolled in the computer, such as a baseball game capable of beingenjoyed on a common monitor while operating the word processor in thepersonal computer TV, an educational program on a real video by the CAI,stress preventing measures for the VDT workers, or a monitor systemusing motion pictures on the computer.

Next, FIG. 19 is a block diagram showing a circuit formultiplex-superimposing the luminance signal.

The luminance signal LSFC outputted from the personal computer isoutputted to the video switch 510 and the voltage comparator 540.

This voltage comparator 540 outputs comparison signals COMP at the highlevel "H" and at the low level "L", respectively, when the luminancesignal LSPC is higher and lower than the reference voltage V_(r).

On the other hand, the superimpose control unit 420 outputs the startingsignal CENBL for making the comparison signal COMP effective to the NANDcircuit 450.

This NAND circuit 450 outputs the starting signal NENBL at the low level"L" only when the comparison signal COMP is at the high level "H" andthe starting signal CENBL is at the high level "H".

An AND circuit 451 is fed with: the starting signal read out from thethree-port video memory 310 for starting the superimpose of theluminance signal LSDA converted by the DAC 410 upon the luminance signalLSPC; the starting signal SSENBL for starting the superimpose of theluminance signal LSDA upon the luminance signal LSPC; and the startingsignal NENBL outputted from the NAND circuit 450.

In response to the change-over signal CNT outputted from the AND circuit451, the video switch 510 superimposes the video signal LSDA upon theluminance signal LSPC.

If the level of the luminance signal LSPC is generated when theluminance signal LSDA is superimposed upon the luminance signal LSPC,the output signal COMP of the voltage comparator 540 takes the highlevel "H".

If, at this time, the superimpose control unit 420 outputs the startingsignal CENBL to the NAND circuit 450, this NAND circuit 450 outputs thestarting signal NENBL at the low level "L" so that the change-oversignal CNT outputted from the AND circuit 451 takes the low level "L"only for the period of the level time of the luminance signal LSPC.

As a result, the luminance signal LSPC in the luminance signal LSDA issuperimposed upon the luminance signal LSMON of the personal computermonitor.

FIG. 20 is a timing chart showing the operations of FIG. 19.

Incidentally, the starting signal SENBL and the starting signal CENBLare set at the high level "H".

The luminance signal LSMON (as shown at (i) in FIG. 20) of the personalcomputer monitor thus obtained is a superimposition of the luminancesignal (as shown at (b) in FIG. 20) LSDA upon the luminance signal LSPC(as shown at (a) in FIG. 20) and a superimposition of letters or specialshapes, which are formed from the luminance signal LSPC during thescanning of the luminance signal LSDA, upon the luminance signal LSDA.

Here, it is needless to say that the aforementioned operations can holdno matter whether the logics might be positive or negative.

Moreover, the AND circuit 451 and the NAND circuit 450 are circuitswhich can be easily realized for all the switches having the switchingfunction such as the OR circuit, the multiplexer or the analog switch.

Although it is general to superimpose the luminance signal LSDA upon theluminance signal LSPC, it takes a remarkably long time to superimposethe luminance signal LSPC upon the luminance signal LSDA, and thesuperimposition is impossible in case the luminance signal LSDA relatesto motion pictures.

In the present invention, however, the letters or special shapes to bedisplayed in the luminance signal LSDA are outputted to the luminancesignal LSPC in the common position of the luminance signal LSDA so thatthe superimposition of the luminance signal LSDA is released only at theportion at the level of the luminance signal LSPC. This raises none ofthe problems of the prior art even in the motion pictures of theluminance signal LSDA and by a remarkably simple circuit. Therefore, thepresent invention is indispensable in the future image processingcircuit.

Next, the operations in case the video still pictures are to beoutputted will be described in the following.

The video signal decoder 140 outputs the vertical synchronizing signalVSTV from the luminance signal LSTV to an AND circuit 810. On the otherhand, the CPU 620 outputs an ON/OFF signal for turning on and off thevideo still pictures to the AND circuit 810.

By outputting the ON/OFF signal at the low level "L" for turning on thestill pictures to the AND circuit 810, the vertical synchronizing signalVSTV is not outputted from the video signal decoder 140 to the verticalwrite line clock generator 224, the vertical write starting counter 225,the vertical write number counter 226, the vertical offset counter 227and the three-port video memory 310.

When the vertical synchronizing signal VSTV is not outputted, thevertical write line clock generator 224, the vertical write startingcounter 225, the vertical write number counter 226, the vertical offsetcounter 227 and the three-port video memory 310 are not set up by thevertical synchronizing signal VSTV.

As a result, the three-port video memory 310 has its writing operationnaturally interrupted because the vertical control system is not reset.

Thus, the CPU 620 can output the control signals of the still picture atany time to enter another job.

In case the still picture is to be turned off, on the other hand, theCPU 620 can output the control signals, if necessary, to the AND circuit810.

There will be required a high-speed processing, in which the CPU 620performs multi-purpose jobs multiplexly, and a loss as high as severaltens mS adversely affects the throughput or turn-round to raise aserious problem.

As a result, the simplified circuit structure according to the presentinvention can eliminate the loss of several tens mS.

What is claimed is:
 1. An apparatus, for use in a computer system havinga CPU, a CPU bus, a display controller, and a display device, fordisplaying at least one video image of variable resolution and positionon said display device, said display device requiring a first verticalsynchronizing signal and a first horizontal synchronizing signal forproducing a display, said apparatus comprising:a) a video decoder thatreceives a composite video signal, separates said composite video signalinto a first luminance signal, a second vertical synchronizing signaland a second horizontal synchronizing signal, and provides said firstluminance, said second vertical synchronizing and said second horizontalsynchronizing signals as outputs; b) an analog-to-digital (A/D)converter, coupled to said video decoder, that receives said firstluminance signal as an input and produces a digital representation ofsaid first luminance signal as an output; c) a video memory, coupled tosaid A/D converter, having first and second read ports and one writeport, said write port being connected to said output of said A/Dconverter, said video memory operable to store said digitalrepresentation of said first luminance signal; d) means, coupled to saidfirst read port of said video memory, for reading out said digitalrepresentation of said first luminance signal from said video memory, tothereby output said digital representation on said CPU bus; and e) avideo mixer, coupled to said second read port of said video memory, forselecting one of a plurality of luminance signals, said pluralityincluding said first luminance signal and a second luminance signalsupplied from said display controller, and producing as an output saidselected luminance signal representing a combination of a first imagerepresented by said first luminance signal and a second imagerepresented by said second luminance signal.
 2. An apparatus, for use ina computer system having a CPU, a CPU bus, a display controller, and adisplay device, for displaying at least one video image of variableresolution and position on said display device, said display devicerequiring a first vertical synchronizing signal and a first horizontalsynchronizing signal for producing a display, said system comprising:a)a video decoder that receives a composite video signal, separates saidcomposite video signal into a first luminance signal, a second verticalsynchronizing signal and a second horizontal synchronizing signal, andprovides said first luminance, said second vertical synchronizing andsaid second horizontal synchronizing signals as outputs; b) ananalog-to-digital (A/D) converter, coupled to said video decoder, thatreceives said first luminance signal as an input and produces a digitalrepresentation of said first luminance signal as an output; c) a videomemory, coupled to said A/D converter, having first and second readports and one write port, said write port being connected to said outputof said A/D converter, said video memory operable to store said digitalrepresentation of said first luminance signal; d) a digital-to-analog(D/A) converter, coupled to said video memory, that receives saiddigital representation signal as an input and produces a reconstructedrepresentation of said first luminance signal as an output; e) a videomixer, coupled to said D/A converter, for selecting one of a pluralityof luminance signals, said plurality including said first luminancesignal and a second luminance signal supplied from said displaycontroller, and producing as an output said selected luminance signalrepresenting a combination of a first image represented by said firstluminance signal and a second image represented by said second luminancesignal.
 3. An apparatus for processing image signals, for use in acomputer system having a CPU, a CPU bus connected to said CPU, a displaycontroller, and a display device, comprising:a video memory formemorizing a given digital image signal, wherein said video memory has awrite port, and first and second read ports, said write port receivingsaid image signal to be memorized in said video memory, said first readport outputting said first image signal; first write control means,connected to said CPU bus, for controlling the writing of said givendigital image signal in said video memory by supplying a first writeaddress to said video memory, a range of said first write address beingspecified with a plurality of write address parameters set by said CPU;a video switch for receiving a plurality of image signals including afirst image signal read out of said video memory and a second luminancesignal supplied from said display controller, and selecting one of saidplurality of image signals to thereby produce a third luminance signalrepresenting a combination of a first image represented by said firstimage signal and a second image represented by said second luminancesignal; and first read control means, connected to said CPU bus, forsupplying said video switch with a first selection signal indicating toselect one of said plurality of image signals, and controlling thereading of said first image signal out of said video memory by supplyinga first read address to said video memory in synchronization with afirst horizontal synchronizing signal and a first vertical synchronizingsignal which are supplied from said display controller, a range of saidfirst read address being specified with a plurality of read addressparameters set by said CPU.
 4. An apparatus for processing imagesignals, for use in a computer system having a CPU, a CPU bus connectedto said CPU, a display controller, and a display device, comprising:avideo memory for memorizing a given digital image signal, wherein saidvideo memory has a write port, and first and second read ports, saidwrite port receiving said image signal to be memorized in said videomemory, said first read port outputting said first image signal; firstwrite control means, connected to said CPU bus, for controlling thewriting of said given digital image signal in said video memory bysupplying a first write address to said video memory, a range of saidfirst write address being specified with a plurality of write addressparameters set by said CPU; a video switch for receiving a plurality ofimage signals including a first image signal read out of said first readport of said video memory and a second image signal supplied from saiddisplay controller, and selecting one of said plurality of image signalsto thereby produce a third luminance signal representing a combinationof a first image represented by said first image signal and a secondimage represented by said second image signal; and first read controlmeans, connected to said CPU bus, for supplying said video switch with afirst selection signal indicating to select one of said plurality ofimage signals, and controlling the reading of said first image signalout of said video memory by supplying a first read address to said videomemory in synchronism with a first horizontal synchronizing signal and afirst vertical synchronizing signal which are supplied from said displaycontroller, a range of said first read address being specified with aplurality of read address parameters set by said CPU; and second readcontrol means, connected to said CPU bus, for controlling the reading ofa fourth image signal stored in said video memory by supplying a secondread address to said video memory, to thereby read out said fourth imagesignal from said second read port of said video memory.
 5. An apparatusin accordance with claim 4, further comprising:a first-in/first-outmemory, connected between said second read port of said video memory andsaid CPU bus, for memorizing said second image signal read out of saidsecond read port, and outputting said second image signal on said CPUbus.
 6. An apparatus in accordance with claim 3, wherein:said selectedimage signal selected by said video switch is supplied to said displaydevice with said first horizontal synchronizing signal and said firstvertical synchronizing signal.
 7. An apparatus in accordance with claim6, further comprising:a digital-to-analog converter, connected betweensaid video memory and said video switch, for converting said first imagesignal read out of said video memory in the form of a digital signalinto a first analog image signal, and supplying said first analog imagesignal to said video switch.
 8. A method of displaying a combination ofa plurality of images on a display device of a computer system having adisplay controller, said method comprising the steps of:providing afirst analog image signal representing a first image of a motionpicture, and a first synchronizing signal; converting said first analogimage signal to a first digital image signal in synchronism with saidfirst synchronizing signal; storing said first digital image signal in avideo memory in synchronism with said first synchronizing signal;reading out said first digital image signal from said video memory insynchronism with a second synchronizing signal which is asynchronouswith said first synchronizing signal; converting said first digitalimage signal read out of said video memory to a second analog imagesignal in synchronism with said second synchronizing signal; selecting,in synchronism with said second synchronizing signal, one of a pluralityof analog image signals including said second analog image signal and athird analog image signal supplied from said display controller, tothereby produce a fourth analog image signal representing a combinationof a second image represented by said second analog image signal and athird image represented by said third analog image signal; and supplyingsaid fourth analog image signal and said second synchronizing signal tosaid display device, thereby displaying said combination of said secondand third images on said display device.
 9. An apparatus for use in acomputer system having a display device and a display controller, fordisplaying a combination of a plurality of images on said displaydevice, comprising:means for receiving a first analog image signalrepresenting a first image of a motion picture, and a firstsynchronizing signal; an analog-to-digital converter for converting saidfirst analog image signal to a first digital image signal; a videomemory for storing said first digital image signal; a first controllerfor controlling the writing of said first digital image signal into saidvideo memory in synchronism with said first synchronizing signal; asecond controller for controlling the reading of said first digitalimage signal from said video memory in synchronism with a secondsynchronizing signal which is asynchronous with said first synchronizingsignal; a digital-to-analog converter for converting said first digitalimage signal read out of said video memory to a second analog imagesignal; a video switch for selecting, in synchronism with said secondsynchronizing signal, one of a plurality of analog image signalsincluding said second analog image signal and a third analog imagesignal supplied from said display controller, to thereby produce afourth image signal representing a combination of a second imagerepresented by said second analog image signal and a third imagerepresented by said third analog image signal, and supplying said fourthanalog image signal to said display device.
 10. A computer systemcomprising:a display device; a display controller for controlling saiddisplay device; means for receiving a first image signal representing afirst image of a motion picture and a first synchronizing signal; avideo memory for storing said first image signal; a first controller forcontrolling the writing of said first image signal into said videomemory in synchronism with said first synchronizing signal; a secondcontroller for controlling the reading of said first image signal fromsaid video memory in synchronism with a second synchronizing signalwhich is asynchronous with said first synchronizing signal; a videoswitch for selecting, in synchronism with said second synchronizingsignal, one of a plurality of image signals including said first imagesignal read out of said video memory and a second image signal suppliedfrom said display controller, to thereby produce a third image signalrepresenting a combination of said first image and a second imagerepresented by said second image signal, and supplying said third imagesignal to said display device.
 11. A computer system comprising:adisplay device; a display controller for controlling said displaydevice; means for receiving a first analog image signal representing afirst image of a motion picture, and a first synchronizing signal; ananalog-to-digital converter for converting said first analog imagesignal to a first digital image signal; a video memory for storing saidfirst digital image signal; a first controller for controlling thewriting of said first digital image signal into said video memory insynchronism with said first synchronizing signal; a second controllerfor controlling the reading of said first digital image signal from saidvideo memory in synchronism with a second synchronizing signal which isasynchronous with said first synchronizing signal; a digital-to-analogconverter for converting said first digital image signal read out ofsaid video memory to a second analog image signal; a video switch forselecting, in synchronism with said second synchronizing signal, one ofa plurality of analog image signals including said second analog imagesignal and a third analog image signal supplied from said displaycontroller, to thereby produce a fourth image signal representing acombination of a second image represented by said second analog imagesignal and a third image represented by said third analog image signal,and supplying said fourth analog image signal to said display device.